Added an SBAPI to get the PythonPath (if the Host knows how to do that). And...

Added an SBAPI to get the PythonPath (if the Host knows how to do that).  And a -P option to the Driver
to print it out.  Changed dotest.py to use that to find the PythonPath it should use given the lldb binary
it was told to run.

llvm-svn: 170932