Add MySQL support to ct-woodpecker.

[jsha]

• Add a DBDriver option to config.
• Import the mysql driver in storage.go.
• Vendor go-sql-driver.
• Add MySQL to Docker

Fixes #82 (we think there may be a crashing bug in the sqlite3 driver).

[coveralls]

Pull Request Test Coverage Report for Build 615

• 23 of 31 (74.19%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.4%) to 68.245%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
monitor/monitor.go	21	29	72.41%
<!--	Total:	23	31	74.19%	-->

Totals
Change from base Build 571:	0.4%
Covered Lines:	836
Relevant Lines:	1225

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💛 - Coveralls

[rolandshoemaker]

Coveralls doesn't like reductions in coverage.

[jsha]

Sounds reasonable. I'll pull it out. I also remembered we should pull in the DB password from a separate file; I'll add that.