Allowed devstack not fail if couldn't stop smb service

Support of nfs and samba services is present for
single-tenant drivers.
By default used multitenant generic driver, that does not use
host's services, so if fail occures with stopping of this service
just go further.

Change-Id: I45e0ffb24f213c7fc68c583951af792d9bfccf39
Merge "Allowed devstack not fail if couldn't stop smb service"