Code review comment for lp:~alan-griffiths/mir/fix-1317370

This doesn't change the situation on my desktop (which is good to begin with, runtime < 1s), but I noticed that the unit test execution time under valgrind increased (vs previous and subsequent runs) for amd64 (https://jenkins.qa.ubuntu.com/job/mir-team-mir-development-branch-utopic-amd64-ci/340/consoleFull), but decreased significantly for armhf (https://jenkins.qa.ubuntu.com/job/mir-team-mir-development-branch-utopic-armhf-ci/338/consoleFull). So overall a net win.

I retriggered the CI just to get extra data points for the timings.