Code review comment for lp:~thumper/juju-core/use-errgo

Reviewers: mp+204604_code.launchpad.net,

Message:
Please take a look.

Description:
Add errgo as a dep, and start using it.

errgo adds the ability to capture the location of
the error creation or annotation. Annotated errors
don't lose the original error.

https://code.launchpad.net/~thumper/juju-core/use-errgo/+merge/204604

(do not edit description out of merge proposal)

Please review this at https://codereview.appspot.com/59930043/

Affected files (+141, -77 lines):
   A [revision details]
   M agent/agent.go
   M agent/tools/toolsdir.go
   M cert/cert.go
   M cmd/juju/bootstrap.go
   M constraints/constraints.go
   M dependencies.tsv
   A dependencies_test.go
   M environs/cloudinit.go
   M environs/cloudinit/cloudinit.go
   M environs/config/config.go
   M environs/configstore/disk.go
   M environs/open.go
   M state/apiserver/charms.go
   M state/apiserver/client/client.go
   M worker/firewaller/firewaller.go