skip 'stop slave' test on windows

Windows does not have os.kill() function, which is used
in the tested code path. Skip the test for now.
Merge branch 'skip-slave-kill' of git://github.com/elmirjagudin/buildbot
SVN source step and Shell command support password obfuscation. Fixes #2468, #1478
Merge branch 'bug2468-squash' of git://github.com/srinupiits/buildbot