Fix locking in LUNetworkConnect()
Fix locking in LUNetworkConnect()

Locks for group instances are aquired only if conflicts are checked.
To this end we must _CheckNodeGroupInstances() only then otherwise
this check will always fail (owned_instances will be []).

Signed-off-by: Dimitris Aragiorgis <4514117c4a99256e19437c7e3407c4ecbf98aec0@grnet.gr>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>

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