environs: move stuff to provider

environs: move stuff to provider

The environs package currently serves two very
different purposes - it is designed to be called into
by external packages (and then it calls into the
registered providers), but it is also used
as a repository for common code shared between
provider implementations.

This dual purpose makes it confusing to see
what's what in the documentation, and also
makes it easy to get the layering abstractions wrong.

This change moves some (probably not all yet)
of the latter code into the provider package,
to make the boundaries more clear.
There was some similar code in the
provider package already.

https://code.launchpad.net/~rogpeppe/juju-core/376-factor-out-provider-utils/+merge/182465

(do not edit description out of merge proposal)

[rog, 2013-08-27 18:43:43]

Please take a look.

[fwereade, 2013-08-28 11:18:21]

LGTM, and I may be confused about the one comment I made.

https://codereview.appspot.com/13269045/diff/3001/environs/testing/polling_te...
File environs/testing/polling_test.go (left):

https://codereview.appspot.com/13269045/diff/3001/environs/testing/polling_te...
environs/testing/polling_test.go:80: 
It sort of looks like this ought to have moved.