CA-116005: validation of the SN mask doesn't appear to be working correctly on the last two values of the mask.
-New IPv4 subnet mask validator added.

Signed-off-by: Gabor Apati-Nagy <gabor.apati-nagy@citrix.com>
CA-116005: validation of the SN mask doesn't appear to be working correctly on the last two values of the mask.
-Unit tests added for Subnetwork mask validation (31 tests)

Signed-off-by: Gabor Apati-Nagy <gabor.apati-nagy@citrix.com>
Merge pull request #124 from GaborApatiNagy/netmask

CA-116005: validation of the SN mask doesn't appear to be working correctly on the last two values of the mask.
Merge branch 'xs64bit' of https://github.com/xenserver/xenadmin into xs64bit-137047