derive custom exceptions directly from Exception

Although StandardError derives from Exception, the python docs for
Exception read:

    All user-defined exceptions should also be derived from this class.

http://docs.python.org/2/library/exceptions.html#exceptions.Exception

Change-Id: If0f009cd0ad5a30329f0f97d869137aeef66af23
Don't duplicate the existing config file list

Make a copy of the original config file list for test_v3.
Otherwise additional tests end up appending to them and corrupting other tests.

Change-Id: I4232956dbfea4b1b7103c751e35112daddc5ff37
initialize environment for tests that call popen

Change-Id: I5b367f7f97de353f12e41dc7768a7fcdc740eabd
Remove unused variables from common.config

These variables were not used, so they've been removed.

Change-Id: I15e7a3f96f00fa46cbbc5132902d0b95d1a4d07c
Merge "derive custom exceptions directly from Exception"
Merge "Don't duplicate the existing config file list"
Merge "initialize environment for tests that call popen"
Merge "Remove unused variables from common.config"