Code review comment for lp:~jameinel/juju-core/bad-formatting-1216285

Reviewers: mp+181983_code.launchpad.net,

Message:
Please take a look.

Description:
environs/tools: print out the correct version

Bug #1216285 is because we were miss-formatting a line about what
version we were filtering. It turns out that while we were printing out
an int as "%s" we were also not priting out what the filter would
actually match. (If you pass a version in that field, we match the exact
version, not just the major version.)

In the process, I realized we don't have much infrastructure for testing
what log messages we are writing, so I added a LogMatches checker. I
think it is something that actually fits better inside the loggo
package, but I wanted to give it some real experience before I tried to
get it into upstream.

https://code.launchpad.net/~jameinel/juju-core/bad-formatting-1216285/+merge/181983

(do not edit description out of merge proposal)

Please review this at https://codereview.appspot.com/12744051/

Affected files:
   A [revision details]
   M environs/tools/tools.go
   M environs/tools/tools_test.go
   A testing/checkers/log.go
   A testing/checkers/log_test.go