added apiserver and api client implemenation of change password.

Added the change-password user command
feedback from review

added more tests to the change-password command
Added --generate and --password flags.

Try to revert the password if the environinfo write fails
client side of NetworkInterfaceWatcher
cleaned up the change-password jenv file interface, simplified the usermanager test

use readpass from latest utils
the first implementation
Refactor Action, per new names.ActionTag changes, and to improve internal structure
Merge remote-tracking branch 'upstream/master' into 122-state-machine-watchinterfaces
changed to WatchCollection
no more TxnRevno exposed in networkInterfacesDoc
update dependencies.tsv to use new names version
use earlier names dependency
Merge pull request #177 from rogpeppe/011-update-names-dep

update dependencies.tsv to use new names version

We want to be able to use the new stuff there.
Uniter Action(id string) API client/server

This commit adds the ability for Uniter clients to query Actions from
state.State by id.  The response includes a server error message if the
Action is not present on the state server.
Test improvements/tweaks
API server Actions is now a batch query.
Check for unit access before querying database
Addressed concerns in Action API PR 140
Action query now uses tags over the wire
Action API query now properly checks validity of request and exercises
error cases