CA-119099: Don't rely on existence of mount point for SR auto-attach

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Signed-off-by: Chandrika Srinivasan <chandrika.srinivasan@citrix.com>
Reviewed-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>
Imported-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>

(cherry picked from commit b643275944d5912305bd9ff2e3f1ee5a0d16b803)

GitHub: closes #126 on xapi-project/sm
CA-95928: Xapi lists and attempts to mount directories as isos

Signed-off-by: Sugandha Aggarwal <sugandha.aggarwal@citrix.com>
Acked-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Vineeth Raveendran <vineeth.thampi@citrix.com>
Imported-by: Thanos Makatos <thanos.makatos@citrix.com>

GitHub: closes #130 on xapi-project/sm
CA-99235: Keep trying to remove the tag forever

In the error handling path of VDI.activate, if the connection with the
master is lost, the slave cannot remove the tag from sm-config. When the
connection is restored, the VDI is left in undefined state. To avoid
this we keep trying to remove the tag until we succeed (the connection
with the host has been restored).

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Vineeth Thampi <vineeth.thampi@citrix.com>
Imported-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>

(cherry picked from commit e32cc329cdd62ec157dc5337c95b06556de62ebd)