Auto merge of #4105 - birkenfeld:master, r=alexcrichton

Do not output "Blocking - waiting for lock" with -q

This is not an error, so it should not be printed unconditionally
to stderr.  Since it can appear intermittently (e.g. due to editor
integration calling build every now and then) it will disturb
things that expect exact output from cargo (e.g. test suites).