CA-95060: Keep trying xenopsd->SMAPI calls until they stop throwing ECONNREFUSED.

If xapi is not running, xenopsd should wait indefinitely for it to
return when trying to make SMAPI calls.

Signed-off-by: John Else <john.else@citrix.com>
CA-95060: Move exception No_storage_plugin_for_sr to storage_interface.ml

This makes it easier to catch for SMAPI clients, since it no longer gets
wrapped in a Storage_interface.Internal_error.

Signed-off-by: John Else <john.else@citrix.com>
Whitespace: Xenops_server_xen.Storage.dp_destroy

Signed-off-by: John Else <john.else@citrix.com>
CA-95060: Ignore Storage_interface.No_storage_plugin_for_sr when calling DP.destroy from xenops.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #976 from jeromemaloberti/CA-95060-tampa-lcm

CA-95060/XOP-228 If a VM shuts down on a slave when xapi is not running, its disks are not deactivated when xapi starts up again