In order to run the the ec2api tempest tests, ec2 credentials have to
be created. This provider creates the ec2 credentials and adds them
to the aws section of the tempest configuration together with some
static configuration that is necessary as well. It also removes
service_available/ec2api parameter from tempest.conf, which actually
has no effect, since the ec2api tempest tests don't evaluate it.
Change-Id: Iab02a6f453de1a07cd059276cb46e23a4b0bb434