ganesha: NFS-Ganesha instrumentation

Introduce the ganesha share driver helper module
which provides the GaneshaNASHelper class from which
share drivers can derive NFS-Ganesha backed protocol
helpers.

Some utility functions are also added to ease
integration.

Partially implements blueprint gateway-mediated-with-ganesha

Change-Id: I8683ea5eb43d7a8eaf0dfa6af3791782d32b944a