docker-compose: Pass --mysql_uri flag to trillian_log_{server,signer}
docker-compose: Pass --mysql_uri flag to trillian_log_{server,signer}

Tells these binaries to connect to the MySQL server running in a Docker
container specified in that same manifest, rather than trying to connect
to a MySQL server running on localhost.

RJPercival/trillian,daviddrysdale/trillian,google/trillian,AlCutter/trillian,daviddrysdale/trillian,Martin2112/trillian,gdbelvin/trillian,daviddrysdale/trillian,gdbelvin/trillian,Martin2112/trillian,Martin2112/trillian,AlCutter/trillian,gdbelvin/trillian,google/trillian,RJPercival/trillian