Log tap filtering

[dmcgowan]

Currently the log tap will return all logs for the requested stream. Usually the compose stream will be tapped and return logs from all applications. Since the client may only care about a single log line or lines from a single compose app, the stream should be able to be filtered on the server end without requiring to store all logs to be searched through. This is likely best implemented as a regexp passed up for the stream since the log tapper should not attempt to understand the format of any of the streams. The log stream would need to be broken up into lines to evaluate the regexp over.