CA-107572: Ignore UUID not found exception during SR scan

VM migration failed because XAPI throw VDI UUID not found exception.
The VDI was already removed, the fix will catch the exception and discard it.

Signed-off-by: Sisimon Soman <sisimon.soman@citrix.com>
Acked-by: Thanos Makatos <thanos.makatos@citrix.com
Imported-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>

(cherry picked from commit d4100048f6a101e62e3d6d677d2ca7213a2016e0)
CA-122950: Ignore invalid VDI handle exceptions in SR.scan

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Zheng Li <zheng.log@citrix.com>
Imported-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>

(cherry picked from commit c75ea33750ae71a20da0db753282b831f69cc5ea)
Merge 'CA-122950' and 'CA-107572' into xs64bit

GitHub: closes #127 on xapi-project/sm