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.
I would be careful with delete_if here.  I believe delete_if modifies the original Array.  If the original Array never gets duplicated on line 13, then you would be modifying the ems.flavors cache directly, which is probably not a good idea.  I think `reject` might be a better method choice.