cmd/juju: user list test is now flexible about durations

The test for the "user list" command was assuming that the creation
and last connection durations for the displayed user would be under a
second. This isn't always true on slowers hosts (e.g. the ppc64
jenkins build slave).

A regex that accepts all possible durations is now used.
Merge pull request #1029 from mjs/userlist-test-robustness

cmd/juju: user list test is now flexible about durations

The test for the "user list" command was assuming that the creation and last connection durations for the displayed user would be under a second. This isn't always true on slowers hosts (e.g. the ppc64 jenkins build slave).

A regex that accepts all possible durations is now used.