Prevent the OVS to OVN migration if any node has the OVS agent
firewall set to "iptables_hybrid". If present, the migration will
exit. This check is implemented in the OVN migration script for
TripleO environments.
Closes-Bug: #1951272
Change-Id: I55f25f56f87bfa2a5e330cdf4c1087e8d4082b29