sigpipe-remote: check for python version earlier in the script

The should abort early, using the wrong python is a pretty bad sign.

Differential Revision: https://phab.mercurial-scm.org/D11078

tests/testlib/sigpipe-remote.py

@@ -7,7 +7,11 b' import subprocess'
 import sys
 import time
 
-# we cannot use mercurial.testing as long as python2 is not dropped as the test will only install the mercurial module for python2 in python2 run
+# we cannot use mercurial.testing as long as python2 is not dropped as the test
+# will only install the mercurial module for python2 in python2 run
+if sys.version_info[0] < 3:
+    print('SIGPIPE-HELPER: script should run with Python 3', file=sys.stderr)
+    sys.exit(255)
 
 if isinstance(sys.stdout.buffer, io.BufferedWriter):
     print('SIGPIPE-HELPER: script need unbuffered output', file=sys.stderr)
@@ -54,10 +58,6 b" def write_file(path, content=b''):"
 
 # end of mercurial.testing content
 
-if sys.version_info[0] < 3:
-    print('SIGPIPE-HELPER: script should run with Python 3', file=sys.stderr)
-    sys.exit(255)
-
 
 def sysbytes(s):
     return s.encode('utf-8')