Modify lldb_suite.py to enable python debugging

Summary:
pudb and pdb interfere with the behavior of the inspect module. calling
`inspect.getfile(inspect.currentframe())` returns a different result
depending on whether or not you're in a debugger. Calling
`os.path.abspath` on the result of `inspect.getfile(...)` normalizes the
result between the two environments.

Patch by Nathan Lanza <lanza@fb.com>

Differential Revision: https://reviews.llvm.org/D49620

llvm-svn: 338923