Merge branch 'CA-183734' into 'master'

Fixing SR free space calculation

In getSRsFreeSpace() method, SR Free space was calculated as ' Utilization - Actual SR size'. This was resulting in negative value.

size = int(self.host.genParamGet("sr", sr, "physical-size"))
            utilisation = int(self.host.genParamGet("sr",
                                                    sr,
                                                    "physical-utilisation"))
            reply[sr] = size - utilisation

Also, This was masking a product issue(Free Space after leaf coalesce is less than the sree space before snapshot).

With my change, job 1199803 is failing because of the above mentioned product issue.

See merge request !31