Don't reopen already open module

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
CA-116814: Correctly calculate shahow_memkb

There was a typo in the divisor and also the units were not converted from MB
to kB.

These values are used for machines without HAP.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #23 from simonjbeaumont/cp-6238

Fix computation of shadow_memkb for HVM domains without HAP