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_based_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.
Merge pull request #543 from mkanoor/bugzilla_1139383

EmsRefresh of Amazon Images for EBS only instances