Introduce getLocalPathBase for MountConnection

Introduce getLocalPathBase in MountConnection so that
class re-using it can override it to present their own
path base.

Change-Id: I9985cb00b8ae7dc4a0ac840d3eb3adadf902d61b
Signed-off-by: Deepak C Shetty <deepakcs@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/12126
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>