Fix Deprecated MySQL Class Name

[turackangal]

Fix #1655

[rnorth]

Sorry but there is #1645 already - though it looks like you may have seen my review comment there and worked around it.

I'd prefer to keep DB specific code out of JdbcDatabaseContainer. Could we instead put all the discovery of the available driver in getDriverClassName()?

e.g. (quickly written pseudocode):

try {
    Class.forName("com.mysql.cj.jdbc.Driver");
	return "com.mysql.cj.jdbc.Driver";
catch (ClassNotFoundException e) {
	return "com.mysql.jdbc.Driver";
}

[rnorth]

Thank you @turackangal - that looks good to me!
I don't think it's really practical to add a unit test for this, so I'm happy with this PR as it is.

Closes #1645, #1655