Make lldb -P work on Windows.

lldb -P, which outputs its python path, works by using Host-layer
facilities to get information about the loaded python module.  This
Host functionality was unimplemented on Windows, so this patch
implements it.  Additionally, it removes a pexpect dependency from
the test runner and uses an equivalent invocation of subprocess.

Reviewed by: Todd Fiala

Differential Revision: http://reviews.llvm.org/D4548

llvm-svn: 213410