Currently this logging implementation is dependent on the order of files
as returned by filepath.Glob, which although internal methods are
documented to be lexographical, does not publicly document this. Here we
defensively resort.
This commit introduces a rotating file logger for Nomad Agent Logs. The
logger implementation itself is a lift and shift from Consul, with tests
updated to fit with the Nomad pattern of using require, and not having a
testutil for creating tempdirs cleanly.
