chore: Expose commit hash in version module

This patch adds a marconi.version.verify_sha() convenience function,
so that continuous integration scripts can use it to verify marconi has
been installed correctly and/or to detect when the installed version is
out of date (i.e., that "import marconi" pulls in the latest version of
the library.)

Change-Id: I645c3a55a837d588fec55fa9b5c1ec579026b8f5