Merge branch 'uniter-context-factory' into uniter-context-factory-2
extract paths from uniter; minor tweaks to juju-run that will hopefully make it a bit less magically action-at-a-distance
Merge branch 'master' of https://github.com/juju/juju into uniter-context-factory-3
address review
Merge pull request #961 from fwereade/uniter-context-factory-3

factor paths out of main uniter type

This was originally just about making the Uniter type look a little bit cleaner (and preparing to make access to some of those paths a little cleaner, for the eventual convenience of the context package), but then the magical correspondence with juju-run became clear. Hopefully the tests on both sides have been fixed such that a change that breaks juju-run will actually lead to test failures.