deploy gerrit server using pre-built binaries

Includes several notable limitations:

* The postgres RDS instance has to be manually created before running the play
* The secure variables have to be defined on the command line
* Gerrit runs on port 8080, instead of 80.  Using 80 is a bit complicated.
* Email doesn't work since I don't know what SMTP server to use (maybe SES?)

Reviewers: @e0d, @gwprice, @cpennington