Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1753219

Description of problem:
In WebUI, when Cluster is not specified, I get:
"Failed to create a compute testvmware (VMware) instance faye-lydick.dell2.lab.eng.bos.redhat.com: undefined method `first' for nil:NilClass"

When Resource pool is not specified, I get:
"Failed to create a compute testvmware (VMware) instance lhellebr-tempthick-def.lab.eng.bos.redhat.com: undefined method `resourcePool' for #<RbVmomi::VIM::Folder:0x00007f982a47f6c0>"

Version-Release number of selected component (if applicable):
Reproduced on Sat 6.6 snap 20.

How reproducible:
Deterministic

Steps to Reproduce:
1. Host -> Create Host
2. Leave {Cluster, Resource pool} empty

Actual results:
Undefined method error

Expected results:
Some user-friendly error