mgr: log module name before PyErr_Print()

mgr: log module name before PyErr_Print()

If an exception is raised in any of the python module functions
invoked by mgr (for example, ImportError if rest_framework isn't
available when serve() in called in the rest module), print the
module name along with the failed method name.

This commit also fixes what looks to me like a missed call to
PyGILState_Release() in the failure case in MgrPyModule::serve().

Signed-off-by: Tim Serong <tserong@suse.com>