CA-129333: Improve debugging for snapwatchd. Add documentation for xslib wrapper.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@citrix.com>

GitHub: closes #92 on xapi-project/sm
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>
CA-135612: Add workaround to avoid waiting on rpcgssd when using NFS4

There currently is a 15s delay when mounting NFS4 shares.
This is BZ#1001934 and has been fixed with a a set of patches upstream.
Blacklisting the kerberos specific module rpcsec_gss_krb5 is the least
intrusive way to work around this with a 3.10 Kernel.

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