[UnitTest] Add very basic tests for NFSSR.py, ISOSR.py and nfs.py

Signed-off-by: Robert Breker <robert.breker@citrix.com>
[Reviewed, cherry-picked and modified for xs64bit from 2b058eb]
Signed-off-by: Mate Lakat <mate.lakat@citrix.com>
CA-135612: Add experimental support for NFSv4 to SM

This enables the specification of the NFS version (3,4) in the device-config of
ISOSRs(type=nfs) and NFSSRs.
E.g. device-config:nfsversion=4

Signed-off-by: Robert Breker <robert.breker@citrix.com>
[Reviewed, improved, cherry-picked and modified for xs64bit from 2b058eb]
Signed-off-by: Mate Lakat <mate.lakat@citrix.com>
[UnitTest] CA-135612: Add tests for nfsversions to NFSSR, ISOSR and nfs

Signed-off-by: Robert Breker <robert.breker@citrix.com>
[Reviewed, cherry-picked from 0d4524d]
Signed-off-by: Mate Lakat <mate.lakat@citrix.com>