Merge pull request #478 from wallyworld/rename-ppc64

Rename ppc64 to ppc64el

Fixes https://bugs.launchpad.net/juju-core/+bug/1349771

simplestreams and maas expect ppc64el, not ppc64
Merge pull request #479 from wallyworld/rename-ppc64-2

Map ppc64 to ppc64el
Merge pull request #509 from wallyworld/rename-ppc64-master

Rename ppc64 to ppc64el

Fixes https://bugs.launchpad.net/juju-core/+bug/1349771

simplestreams and maas expect ppc64el, not ppc64