test: stabilize bundle generation for test-sparse-revlog.t

To reduce the instability in the bundle binary content, we force it to contains
delta against p1 in all cases.

In the previous changeset, we already stabilized the processing of the bundle.
So we don't see any output change in the test itself.

tests/artifacts/cache/big-file-churn.hg.md5

@@ -1,1 +1,1 b''
-403f5c247ad7cf58d3fad247a6b5e731
+cb1e67ae6b17ba66dd455f9782692f4a

tests/artifacts/scripts/generate-churning-bundle.py

@@ -1,139 +1,139 b''
 #!/usr/bin/env python
 #
 # generate-branchy-bundle - generate a branch for a "large" branchy repository
 #
 # Copyright 2018 Octobus, [e-mail]
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 #
 # This script generates a repository suitable for testing delta computation
 # strategies.
 #
 # The repository update a single "large" file with many updates. One fixed part
 # of the files always get updated while the rest of the lines get updated over
 # time. This update happens over many topological branches, some getting merged
 # back.
 #
 # Running with `chg` in your path and `CHGHG` set is recommended for speed.
 
 from __future__ import absolute_import, print_function
 
 import hashlib
 import os
 import shutil
 import subprocess
 import sys
 import tempfile
 
 BUNDLE_NAME = 'big-file-churn.hg'
 
 # constants for generating the repository
 NB_CHANGESET = 5000
 PERIOD_MERGING = 8
 PERIOD_BRANCHING = 7
 MOVE_BACK_MIN = 3
 MOVE_BACK_RANGE = 5
 
 # constants for generating the large file we keep updating
 #
 # At each revision, the beginning on the file change,
 # and set of other lines changes too.
 FILENAME='SPARSE-REVLOG-TEST-FILE'
 NB_LINES = 10500
 ALWAYS_CHANGE_LINES = 500
 FILENAME = 'SPARSE-REVLOG-TEST-FILE'
 OTHER_CHANGES = 300
 
 def nextcontent(previous_content):
     """utility to produce a new file content from the previous one"""
     return hashlib.md5(previous_content).hexdigest()
 
 def filecontent(iteridx, oldcontent):
     """generate a new file content
 
     The content is generated according the iteration index and previous
     content"""
 
     # initial call
     if iteridx is None:
         current = ''
     else:
         current = str(iteridx)
 
     for idx in xrange(NB_LINES):
         do_change_line = True
         if oldcontent is not None and ALWAYS_CHANGE_LINES < idx:
             do_change_line = not ((idx - iteridx) % OTHER_CHANGES)
 
         if do_change_line:
             to_write = current + '\n'
             current = nextcontent(current)
         else:
             to_write = oldcontent[idx]
         yield to_write
 
 def updatefile(filename, idx):
     """update <filename> to be at appropriate content for iteration <idx>"""
     existing = None
     if idx is not None:
         with open(filename, 'rb') as old:
             existing = old.readlines()
     with open(filename, 'wb') as target:
         for line in filecontent(idx, existing):
             target.write(line)
 
 def hg(command, *args):
     """call a mercurial command with appropriate config and argument"""
     env = os.environ.copy()
     if 'CHGHG' in env:
         full_cmd = ['chg']
     else:
         full_cmd = ['hg']
     full_cmd.append('--quiet')
     full_cmd.append(command)
     if command == 'commit':
         # reproducible commit metadata
         full_cmd.extend(['--date', '0 0', '--user', 'test'])
     elif command == 'merge':
         # avoid conflicts by picking the local variant
         full_cmd.extend(['--tool', ':merge-local'])
     full_cmd.extend(args)
     env['HGRCPATH'] = ''
     return subprocess.check_call(full_cmd, env=env)
 
 def run(target):
     tmpdir = tempfile.mkdtemp(prefix='tmp-hg-test-big-file-bundle-')
     try:
         os.chdir(tmpdir)
         hg('init')
         updatefile(FILENAME, None)
         hg('commit', '--addremove', '--message', 'initial commit')
         for idx in xrange(1, NB_CHANGESET + 1):
             if sys.stdout.isatty():
                 print("generating commit #%d/%d" % (idx, NB_CHANGESET))
             if (idx % PERIOD_BRANCHING) == 0:
                 move_back = MOVE_BACK_MIN + (idx % MOVE_BACK_RANGE)
                 hg('update', ".~%d" % move_back)
             if (idx % PERIOD_MERGING) == 0:
                 hg('merge', 'min(head())')
             updatefile(FILENAME, idx)
             hg('commit', '--message', 'commit #%d' % idx)
-        hg('bundle', '--all', target)
+        hg('bundle', '--all', target, '--config', 'devel.bundle.delta=p1')
         with open(target, 'rb') as bundle:
             data = bundle.read()
             digest = hashlib.md5(data).hexdigest()
         with open(target + '.md5', 'wb') as md5file:
             md5file.write(digest + '\n')
         if sys.stdout.isatty():
             print('bundle generated at "%s" md5: %s' % (target, digest))
 
     finally:
         shutil.rmtree(tmpdir)
     return 0
 
 if __name__ == '__main__':
     orig = os.path.realpath(os.path.dirname(sys.argv[0]))
     target = os.path.join(orig, os.pardir, 'cache', BUNDLE_NAME)
     sys.exit(run(target))