UI Provision code to filter Amazon instance types

https://bugzilla.redhat.com/show_bug.cgi?id=1133780

The instance types are filtered based on the virtualization
type specified in the AMI. Each instance can support 1 or more
kind(s) of virtualization: hvm, paravirtual. Each AMI has a
virtualization type, so based on the selected AMI we can whittle
down the list of applicable instance types.
I'm not saying remove the check, I'm saying match the checking style to what's already there for architecture.

One of:
- Move the virt check up to line 9 next to the architecture one.
- Move the architecture check down to line 10 as a trailing if

Also one of
- Change the check for virtualization_type to check for specifically hvm and paravirtual like is done for arhcitecture
- Use respond_to? instead of checking specific values for both architecture and virtualization type.