Merge multiple improvements to multipath.conf

Signed-off-by: Germano Percossi <germano.percossi@citrix.com>

GitHub: closes #146 on xapi-project/sm
CA-134864: Fix plugin call for SXM.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Reviewed-by: Chandrika Srinivasan <chandrika.srinivasan@citrix.com>

GitHub: closes #175 on xapi-project/sm
CA-130987: Forward any exceptions thrown inside _snapshot

Signed-off-by: Vineeth Raveendran <vineeth.thampi@citrix.com>
Reviewed-by: Chandrika Srinivasan <chandrika.srinivasan@citrix.com>
Imported-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Reviewed-by: Mate Lakat <mate.lakat@citrix.com>

(cherry picked from commit 6d7cf76dc400fbc4c8ccafddf72131c65724da67)

GitHub: closes #195 on xapi-project/sm
UnitTest: tests for NFSSR.py, ISOSR.py and nfs.py

Test mount calls.

Signed-off-by: Robert Breker <robert.breker@citrix.com>
Signed-off-by: Mate Lakat <mate.lakat@citrix.com>
Acked-by: Germano Percossi <germano.percossi@citrix.com>

(cherry picked and slightly adapted from commit 27fbd54)
Imported-by: Robert Breker <robert.breker@citrix.com>
CA-135612: Add experimental support for NFSv4

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

For example:

    device-config:nfsversion=4

Signed-off-by: Robert Breker <robert.breker@citrix.com>
Signed-off-by: Mate Lakat <mate.lakat@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>

(cherry picked from commit 7fa6b8c)
Imported-by: Robert Breker <robert.breker@citrix.com>
CA-135612: [UnitTest] Tests for nfsversions

Test NFSSR, ISOSR and nfs

Signed-off-by: Robert Breker <robert.breker@citrix.com>
Reviewed-by: Mate Lakat <mate.lakat@citrix.com>
Acked-by: Germano Percossi <germano.percossi@citrix.com>

(cherry picked and rebased from commit 7c13c87)
Imported-by: Robert Breker <robert.breker@citrix.com>
CA-141409: Default to using NFS version 3 again

We were unintentionally using nfsversioni 4 on trunk.
This was because the command mount.nfs defaults to using nfsversion 4 instead
of version 3 in our environment on trunk, despite it's documentation claiming
otherwise.
This commit specifies the nfsversion additionally in the mount options, to make
sure that we default to nfsversion 3 again, and that the default setting can
be switched intentionally.

Signed-off-by: Robert Breker <robert.breker@citrix.com>
CA-141409: [UnitTest] Updated unittests to default to using NFS version 3 again

Signed-off-by: Robert Breker <robert.breker@citrix.com>