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.
@Fryguy 
Is virtualization type guaranteed to be there for every instance. If an ems_refresh has not run the virtualization type column would not be filled in.