run-tests.py: avoid using popen2.Popen4 - use subprocess instead
Use subprocess to emulate Popen4 if available - similar to how it is done in
util.py.
Using popen2 under python 2.6 gives
DeprecationWarning: The popen2 module is deprecated. Use the subprocess module.
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added 1 changesets with 4 changes to 4 files
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4 files updated, 0 files merged, 0 files removed, 0 files unresolved