vdsm: Use UUID as unique identifier for socket names

To avoid issues with limitation on the length of paths to UNIX Domain sockets
we're changing the behavior to use the UUID of the VM.

Additionally for backwards compatiblity we're making a symlink of the old name
if it not already exists.

Change-Id: I8f12a6b5ac641686ad29dc17a9f214ee82b3b2cf
Bug-Url: https://bugzilla.redhat.com/918536
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/13220
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Peter V. Saveliev <peet@redhat.com>
Reviewed-by: Peter V. Saveliev <peet@redhat.com>