Parse gtmroutines env. variable

Added python script that parses the gtmroutines environment variable to fetch
possible GT.M source paths and prints it to stdout.
CMake executes this script and picks up the stdout to provide the user with a
list of options for the MUnit routines import directory.

Change-Id: Id9e8caeb34c0c16b2ab7573aca56677dfdfb0c20