EmsRefresh of Amazon Images for EBS only instances

https://bugzilla.redhat.com/show_bug.cgi?id=1139383

This is the first part of the ticket, it pertains to storing the
block_storage_only for flavors and root_device_type for images.
Once this data is filled in by the ems_refresh we will be able to
filter out invalid instance types during provisioning.
@roliveri Can you comment on the column name choice here?  Hoping you can help since this at the database level we are trying to abstract the names across Amazon and Openstack.  Basically, certain flavors do not support instance_store volumes (hence the thought behind `block_storage_only?`.  Is that even a thing on Openstack?