Use syslog to capture the build log

[jawher]

Replaces the old way of capturing logs (stream docker logs to a pipe with a scanner on the reader to write to mongo) with a new one based on docker's syslog logging driver.

• The server listens for TCP connections on port 3001
• Build containers are started configured to stream their logs to that endpoint (tcp:https://server:3001) using the syslog driver and format
• The server parses and stores the logs in mongo

For this feature to work, the server needs to know its address, so that when it starts an orchestration container, it can configure it with the syslog endpoint.
This is set in the BZK_SYSLOG_URL in the server.
The CLI was modified to set that variable from the --syslog-uri flag (which has a default value of $BZK_SYSLOG_URL in the host).
For example:

bzk service start --syslog-uri="tcp:https://$(docker-machine ip main):3001"

[jawher]

BTW, I'm not very happy with the --syslog-uri flag: to start the server, we need to pass to it its uri (host and port). This will make the server incompatible stuff like docker run -P or any other auto port mapping.

However, since this is just an intermediary step toward separating the concrete build part in a separate component (See #260), this problem will be solved in the next iteration, where this server uri will be passed to the worker component instead of the server.

[julienvey]

👍