This also includes an initial pass at letting people set minimum levels.
But it's a little more complex than I'd like, so will delete in the next
commit.

Make sure comments refer to Gitlab, not Github. The Exchange
function gets enough data from Gitlab OAuth that it doesn't
need the kludge the Github method required.

Replace authurl, tokenurl and baseurl with just the one: siteurl.
The rest can be derived.

Now trying to get group = X case.

Number of issues fixed: needed a baseurl option, needed to use the
gitlab api NewOAuthClient call.

Made authurl/tokenurl optional.  All *url's default to gitlab.com urls.

* Allow tests to specify mysql connection info.

User can set MYSQL_TEST_USER, MYSQL_TEST_PASS and MYSQL_TEST_HOST
environment variables for test environments that need that.

* Changes from testing.

Need to set both time fields as '0000-00-00' depends on a feature
deprecated in MySQL 5.7.4.

Go lint wanted snake case for my sql_config var. sqlConfig it is.

* Go go idioms.

Based on feedback from Niall, a cleaner way to do this in Go.

Network is insanely slow tonight (hello snow). So building this to
cache the install of mysql-client and the install of golint.
The latter issue was noted and deliberately not fixed in
https://github.com/docker-library/golang/issues/102 .

Sigh.

Add mysql client to go container.
Use correct params with mysql db init step.

Fix newly-broken tests

Simplify key generation