Description of problem:
There is no bare metal option to select in the "Deploy On" field when creating or updating a child host group and its parent host group is set to use a compute resource.

Steps to Reproduce:
1. Create a top most parent host group and set the "Deploy On" to any compute resource.
2. Create a child host group which inherit the above parent host group.

Actual results:
Missing "Bare Metal" or blank option in the "Deploy On" select box

Expected results:
Able to select Bare Metal

Additional info:

I think is the cause of the issue:

Unset/Blank value serves different purpose in the uppermost parent host group and child host group.

• For parent host group unset/blank value means set "Bare Metal" as the compute resource.
• For child host group unset/blank value means inherit the value from parent host group.

Due to this conflict, we are unable to set "Bare Metal" in the child host group.