* 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

Use functions to build key generation options.
Make it entirely optional.

sqlite uses CGO which prevents the building of statically-linked binaries.
This change will omit sqlite support when building a static binary with:
CGO_ENABLED=0 go build --ldflags '-extldflags "-static"'

When configured the server will request a TLS certificate for the specified server name from LetsEncrypt