Added basic doc for HA
Added singleton and voting sections and corrected

I addressed several redaction issues and added sections for
voting and singleton workers as commented by @rogpeppe
Made gramatical corrections suggested by @mjs
added dry run support for upgrade-juju
simplified upgradejuju dry run test
changed upgrade-juju dry run option to --dry-run
Added note on singleton vs concurrent

After talking with @fwereade I added a note explaining that
singletons, as they are documented righ now, are only a reflection
of current status but should be considered as wrong and will be
re-implemented properly, as concurrent workers, in the future.
Corrected two gramatical errors
added test for call dispatching
made the test more standard conform
Merge branch 'master' of https://github.com/juju/juju into fix-api-params

# By Ian Booth
# Via Ian Booth (1) and Juju bot (1)
* 'master' of https://github.com/juju/juju:
  Tweak hpcloud boilerplate to turn floating-ip and remove az from example region
Merge branch 'master' of https://github.com/juju/juju into fix-api-params
added log to intruct the user how to run this command to update to a particular version
made output prettier based on fwereade's feedback
Display welcome message when starting debug-hooks sessions.
removed commented out line in upgradejuju_test
Merge branch 'master' of https://github.com/juju/juju into fix-api-params
state/machine: use WaitAgentPresence, rename AgentAlive
state/machine: StartSync in SetAgentPresence
state/machine: check IsManager and only Sync presence watcher