main.get_hosts_supporting_aws: Ignore --ec2tags if not supplied.
main.get_hosts_supporting_aws: Ignore --ec2tags if not supplied.

Without this check, we forward an empty tagdict to get_by_tagvalue.
Empty tag dict fetches all hosts. It does not, in any case, make any
sense to do a tag-query when we have not requested it using --ec2tags.

espenak/awsfabrictasks,jneves/awsfabrictasks,espenak/awsfabrictasks,jneves/awsfabrictasks