Wrote initial outlining of the API Implementation Guide.
Added organizational aspects.
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Added versioning and first pattern.
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Updated versioning section.
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Changed guide for API versioning implementation and testing (different approach, better example). Section about bulk requests is still WiP.
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Rewrote section about bulk requests.
Merge branch 'master' of https://github.com/juju/juju into api-implementation-guide
Changes after review.
Introduce apt-mirror config attribute

And propagate it through to environs/cloudinit.
Exluding provisioner tests for ppc and arm archs as gcc report compiler errors.

 GCC has been fixed but are not yet available.
cloudinit/sshinit: configure apt mirror

sshinit is updated to rewrite APT sources
if a mirror is specified. We perform the
same actions as cloud-init would perform,
but via shell commands instead of using
cloud-init directly.
Taken review comments into consideration.