CA-74544: Associate a username with the sessions xapi passes to SM backends.

This will appear in the audit log. Formatting is consistent with the
"__dom0__vmpr" username associated with the session passed to the VMPR
plugin.

Signed-off-by: John Else <john.else@citrix.com>
CA-96893: Remove metadata from xenopsd after a suspend.

Previously metadata was only removed after a shutdown.

Signed-off-by: John Else <john.else@citrix.com>
CA-96893: VM.remove now also removes the VmExtra persistent data.

Signed-off-by: John Else <john.else@citrix.com>
CA-97297: ErrorMsg - Cannot remove parameters from read-only map
Create new module: Storage_utils

Signed-off-by: John Else <john.else@citrix.com>
CA-98492: Fix for VDI.create for certain VDI types

SM was using a Record_utils function to determine the type of new VDIs
and defaulting to the "user" type, which meant that redo_log and HA
statefile VDIs would erroneously be created as "user" VDIs.

Signed-off-by: John Else <john.else@citrix.com>
CA-98936: Stop xapi from creating files in /tmp every time it gets an update from xenopsd

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #1014 from johnelse/ca-98492

CA-98492: Fix for VDI.create for certain VDI types
Merge pull request #1016 from johnelse/ca-98936

CA-98936: Stop xapi from creating files in /tmp every time it gets an update from xenopsd
Merge pull request #1012 from siddharthv/CA-97297

CA-97297: ErrorMsg - Cannot remove parameters from read-only map
Merge pull request #1011 from johnelse/ca-96893

CA-96893: Remove xenopsd VmExtra metadata from filesystem after suspend and migrate.
Merge pull request #1005 from johnelse/ca-74544

CA-74544: Associate a username with the sessions xapi passes to SM backends.