Some small improvements to the fake hypervisor
Some small improvements to the fake hypervisor

This patch modifies the fake hypervisor to substract the memory “used”
by “running” instances from the free memory, so the actual node
information changes based on the running instances.

Also some style changes and fixes are added.

Reviewed-by: ultrotter

andir/ganeti,onponomarev/ganeti,apyrgio/snf-ganeti,dimara/ganeti,apyrgio/ganeti,yiannist/ganeti,ganeti/ganeti,mbakke/ganeti,grnet/snf-ganeti,ganeti/ganeti,grnet/snf-ganeti,yiannist/ganeti,apyrgio/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,andir/ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,dimara/ganeti,mbakke/ganeti,apyrgio/snf-ganeti,leshchevds/ganeti,leshchevds/ganeti,andir/ganeti,bitemyapp/ganeti,onponomarev/ganeti,bitemyapp/ganeti,yiannist/ganeti,ganeti/ganeti