Update juju/utils dependency and fix vet warnings

Bump juju/utils to latest version for lp:1367896 fix. Also
fix go vet warnings in state/upgrades.go debug messages.
Merge pull request #877 from bz2/utils_dep_bump

Update juju/utils dependency and fix vet warnings

Bump juju/utils to latest version for lp:1367896 fix. Also
fix go vet warnings in state/upgrades.go debug messages.

http://reviews.vapour.ws/r/140/