CA-149027: Refactor XenCert messages for trim test

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
CA-149027: Update xencert-guide for space reclamation test.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
CA-149027: Update verification form for space reclamation tests.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>