test/end-to-end: give GitLab more time to start
GitLab does not always finish starting after the 15 seconds we were
waiting. Wait for 60 seconds instead to make it more consistent.
In particular, /var/log/gitlab/gitaly/current
shows that Gitaly
is started, stopped, and then re-started, and the second start does
not occur until about 45 seconds into our wait.