LUVerifyCluster: Fix bug with offline nodes
LUVerifyCluster: Fix bug with offline nodes

[…]
 * Other Notes
   - NOTICE: 1 offline node(s) found.
 * Hooks Results
Failure: command execution error:
iteration over non-sequence

Commit a0c9776a introduced an error simulation mode to LUVerifyCluster.
Due to a small mistake, offline nodes weren't skipped when checking the
results of verification hooks and iterating over None raises an
“iteration over non-sequence” error.

Signed-off-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>
Reviewed-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>

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