Port the round-trip test server to MySQL.
- Also ported importJson to mysql.
- Commit results and stats correctly.
- Don't use (for now) the new claimPage function, as it doesn't record the
commits.
- Pass connection parameters as command line options.

TODO:
- Improve performance, possibly using transactions.
- Record performance numbers (bug #46659).
- Remove debugging output.
Bug: 44652

Change-Id: I25ef1f909308676e311180c9cdfceca7f91118fb