reopen implementation for the FileLogger

we need to make note of the current loglevel, as it may not be the version from
the config file that start will assert
MCO-328 hook SIGWINCH to Log.reopen

USR1 and USR2 are already taken, so we're left with SIGWINCH.  SIGWINCH is sent
when the terminal driver detects that the terminal has changed size, and is
most applicable to full-screen console applications.