Makes room to make the tests more like ruby tests, which will be
employed heavily.

Instead of running integration tests directly in Go, we run it in Ruby
by calling Ghostferry as a subprocess. The idea is that we will be able
to test the interrupt/resume work more easily as well as making
integration tests easier to write.

In order to allow the ruby tests to inject race conditions for testing
purposes, we need a way for the ruby code to pause and restart the
execution of Go code at strategic locations. This is done with a local
Unix socket. At locations of interests, the Go code will send some
string via the Unix socket to the Ruby code. The ruby code will perform
some sort of callback (such as injecting data, or locking a row) and
then send a command back to the Go code via the same Unix socket,
allowing it to continue executing. Note that each time we send some
status to the ruby server, we do it in a new connection. This is to
avoid race conditions if one shared connection was used between all the
goroutines we employ inside Ghostferry.

Stdout and stderr are captured and they can be asserted
against/examined, more helper methods can be created later to give
better structures for the stdout/stderr output such as being able to
recognize a panic, or recognize particular stages of execution from
within the logs.

Lastly, the intention is to replace all integration tests with this
framework in the future as it would likely be more robust and cause less
issues such as goroutine leaks during the go test run. However, for the
time being we will have both integration tests in Go and Ruby.

The DataWriterHelper is a straight port from data_writer.go, which is a
multithreaded data writer that writes random data to the database.

The DbHelper helps connects to the database, seed it, and verify that
the source matches the target so that tests don't have to implement it
over and over again.

Added some trivial integration tests and some interrupt/resume tests.

Note the interrupt and resume works on master as of this commit without
reconciler because the schema didn't change.