Implement diskmanager worker
worker/diskmanager: add tests
api/diskmanager: add tests
apiserver/diskmanager: add tests
Fix worker/diskmanager interface; fix vet warning

Make version.OSType a Stringer so it can be used as
argument to %s in printf functions.
cmd/jujud: remove diskmanager worker

Will add this back in in a follow-up.
storage: add package docs, fix comments
Handle 404 in maasEnviron.StopInstances
implemented metric validation prior to storing
make validate a method on the metricBatch
review comments fixed and fixed unit tests
Retry release individually in certain cases
state/multiwatcher: move remaining mutliwatcher related types
tests pass
remove unused types
remove vestigial type decl
Merge pull request #1109 from waigani/migrate-network

State Upgrade Step: Add EnvUUID to Network docs

Add three upgrade steps. The first two prepend the envuuid to the _id of networks and requestedNetworks doc as well as add a env-uuid field. The third step only adds the env-uuid field to the networkInterfaces doc.

Update helper functions in state/upgrades_test.go to support optionally add only the env-uuid field, leaving the original _id value.
tests pass
Address review comments
update to new utils hash