lib/streamer: add tailReader util.
lib/streamer: add tailReader util.

Needed for some parts of runc log handling coming up shortly.

Signed-off-by: Eric Myhre <2346ad27d7568ba9896f1b7da6b5991251debdf2@exultant.us>

heavenlyhash/r200,heavenlyhash/r200,polydawn/repeatr,polydawn/repeatr