PR-1291: Initial Commit for OCFS2 SR Offering
CP-4526: Fix SR.scan.
CP-4523:  Storage Thin Provisioning: Handle OCFS2 failure

Added new OCFS specific errors and covered all error paths in OCFS operations.
CA-113313: Limiting the OCFS SR offering to OCFSoHBA and OCFSoISCSI.
CA-113314: Fixed OCFSoHBA scan error, added 3rd unused arg to vdi(),
ref. FileSR
CA-113315: Zeroing out is not needed as we allow destroy only when there
are no vdis.
CA-113316: Added snapshot and clone attributes to CAPABILITIES
CA-113315: zeroout the filesystem metadata to override existing FS check
CA-113313: Add OCFS pluggin in Makefile to pick OCFSSR.py file
CA-113317: Add multipath functionality to ocfsohba
CA-113313: Removed OCFSSR after the link creation that happens in loop
PR-1291: Added ocfsoiscsi and ohba to mpath, to store path details in
PBD. Also added a dummy probe mechanism in OCFSSR
PR-1291: addressed review comments
Merge git://hg.uk.xensource.com/carbon/pr-1291/sm into PR-1291