HPCC-9771 Configmgr - crashes when deleting 'null' roxie server

  - remove 'null' servers from new instances

Signed-off-by: Gleb Aronsky <gleb.aronsky@lexisnexis.com>
Merge pull request #4694 from garonsky/issue-9771_null_in_roxie_server

HPCC-9771 Configmgr - crashes when deleting 'null' roxie server

Tested by Chris.