CA-189186: Fixed Unit Tests for trim_util.py
CA-189186: Fixed Unit Tests for trim_util.py

Trim has been modified to use blkdicard in place of lvremove with
issue_discards=1. Test case has been modified accordingly.

Signed-off-by: Pritha Srivastava <pritha.srivastava@citrix.com>
Reviewed-by: Stefano Panella <stefano.panella@citrix.com>

GitHub: closes xapi-project/sm#290

xapi-project/sm,pritha-srivastava/sm,kostaslamda/sm,pritha-srivastava/sm,germanop/sm,germanop/sm,chandrikas/sm,kostaslamda/sm,chandrikas/sm,kostaslamda/sm,xapi-project/sm,germanop/sm,pritha-srivastava/sm,xapi-project/sm,chandrikas/sm