maint - fix visibility of Logger::Base#start and log

start and log are parts of the public api of Logger plugins

Logger#start is invoked by MCollective::Log#configure
Logger#log is invoked by MCollective::Log#log

As such these virtual methods should not be considered part of
MCollective::Logger::Base's private api.
MCO-328 add reopen to Logger::Base

Here we add the reopen method to the Logger api.  This will be used to have the
logger reopen the logfiles on signal, for better interaction with logrotate.
MCO-328 Add Log.reopen that just delegates to @logger.reopen

Loggers are not used raw by the rest of the codebase, but via their owner
MCollective::Log.  Here we expose the Logger#reopen method through the
MCollective::Log class
maint - add basic file_logger_spec.rb

Here we add some basic testing to File_logger.   There's not much
to test, as most of File_logger simply delegates to ::Logger.
MCO-328 Implement reopen for File_logger
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.
Merge pull request #218 from richardc/MCO-328_reopen_logs_on_signal

MCO-328 reopen logs on signal