host/logbuf: Don’t leak log tailers

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Godeps: Use our fork of ActiveState/tail

This is a temporary measure until
ActiveState/tail#42 with StopAtEOF is merged.

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
host/logbuf: Fix race during close

When the log file is closed, any readers should read until the EOF so
that they don’t miss lines.

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>