Description of problem:
Custom fencing settings are not saved in DB

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1.Add custom PM agent for example :
2.engine-config -s CustomVdsFenceType="virsh"
3.engine-config -s CustomVdsFenceOptionMapping="virsh:port=port,secure=ssh"
4.Run application
5.Add two hosts h1 and h2
6.Select PM for h1 with the new "virsh" agent and address/user/password 
7.Press OK

Actual results:

Operation Canceled
Error while executing action:
cascade:
Cannot edit Host. Selected Power Management Agent is not supported.


Expected results:
Custom PM agent settings should be saved in DB

Additional info:
Validation should take into account new custom agents added by engine-config