Column families and other small improvements

[julienatshopify]

Problem

This docker image is useful for integration tests. However, the first thing every test must do is create the necessary tables and column families. It would be very convenient to be able to specify which tables and column families are necessary at startup, so no special build or test logic is required.

Solution

Add an optional -cf flag allowing to specify which tables and column families to be created at startup.

Result

The user can just specify what needs to be created at startup:

docker run -d -p 8080:8080 spotify/bigtable-emulator  -cf dev.records.data,dev.records.meta

This would create data and meta column families in the records new table in the dev instance.

This PR is also adding small improvements:

• the log line bttest.Server running on [::]:8080 appear at startup so users can wait for this line to appear in docker logs instead of waiting an arbitrary number of seconds after launching the server.
• the makefile is removing the test container after the test in order to not pollute Docker.
• when an error occur, the details are printed in the standard error stream.

@rgruener

[julienatshopify]

It seems there is no interest.