Now that the tests work in py2 or p3 we don't set py version in AP. This
allows for dealing with the AP images that don't have a way to set the
py version.
Related changes:
* BoostBuild.Tester & TestCmd.TestCmd interfaces now accept external process parameters as a list of strings, thus avoiding problems with parsing arguments containing spaces.
* Avoided a potential process hang in case an external process being run prints out enough output to fill up the OS's pipe buffer (OS would pause the process until someone read the data from the pipe but the testing framework would not do this until the process in question had terminated).
[SVN r79448]
