tests: mock getpid to reduce glob usage

With util.getpid, it is now possible to define fixed pids.

Future iterations can define a map of pids on a locked
first come first serve basis to create a more realistic
harness, but for now this is good enough.

This applies to blackbox, but could apply to other
tests as well.

tests/mockblackbox.py

@@ -4,8 +4,11 b' def makedate():'
     return 0, 0
 def getuser():
     return 'bob'
+def getpid():
+    return 5000
 
 # mock the date and user apis so the output is always the same
 def uisetup(ui):
     util.makedate = makedate
     util.getuser = getuser
+    util.getpid = getpid

tests/test-blackbox.t

@@ -108,7 +108,7 b' backup bundles get logged'
   saved backup bundle to $TESTTMP/blackboxtest2/.hg/strip-backup/*-backup.hg (glob)
   $ hg blackbox -l 6
   1970/01/01 00:00:00 bob (*)> strip tip (glob)
-  1970/01/01 00:00:00 bob (*)> saved backup bundle to $TESTTMP/blackboxtest2/.hg/strip-backup/*-backup.hg (glob)
+  1970/01/01 00:00:00 bob (*)> saved backup bundle to $TESTTMP/blackboxtest2/.hg/strip-backup/73f6ee326b27-7612e004-backup.hg (glob)
   1970/01/01 00:00:00 bob (*)> updated base branch cache in * seconds (glob)
   1970/01/01 00:00:00 bob (*)> wrote base branch cache with 1 labels and 2 nodes (glob)
   1970/01/01 00:00:00 bob (*)> strip tip exited 0 after * seconds (glob)