Create new _SafeShutdownInstanceDisks function
Create new _SafeShutdownInstanceDisks function

This new function checks whether an instance is running, before shutting
down its disks. This is what the Exec() of LUDeactivateInstanceDisks
did, so that is replaced by a call to this function.

Reviewed-by: iustinp


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