Ensure we generate unique usernames otherwise validations fail

What does this MR do?

1. We were still using FFaker in db/fixtures/development/18_abuse_reports, no more!
2. I didn't apply the fix from https://gitlab.com/gitlab-org/gitlab-ce/commit/bf69e6291d7c7029c18f21a65abc2579e1825cb0 to spec/requests/api/v3/members_spec.rb, it's done now!

@smcgivern This is fixing master! :)

assigned to @smcgivern

approved this merge request

I think the CE -> EE failure is because https://gitlab.com/gitlab-org/gitlab-ce/commit/5388bb1cca501442be05ddf929fae7d1bfcbd1f7 isn't in EE yet.

merged

mentioned in commit 5f7ebfb9