Add source code context information to debug logs
    
    The log.debug() function helpfully adds the name of the function
    invoking it but in a complicated software package there are many
    functions/methods which share the same name. Thus a debug message
    like this:
    
    DEBUG(__init__): xxx
    
    does not give you much context, there are probably hundreds of
    __init__ methods. It would help to qualify the method name which it's
    class name, that gives a lot more context when reading the
    log. Sometimes it's also helpful to know the file and line number.
    
    This patch adds the class name to the function and included the
    filename and line number as well. The file path is trimmed to the last
    3 components, sufficient to give context but not too verbose. Now the
    debug message might look like this instead:
    
    DEBUG(ipsilon/providers/common.py:129 LoadProviders.__init__()): xxx
    
    Also included is a config option 'stacktrace_on_error' which will
    include a stacktrace when the log.error function is called. It can be
    very useful to see a stacktrace when logging an error, it defaults to
    off.
    
    Signed-off-by: John Dennis <jdennis@redhat.com>
    Reviewed-by: Simo Sorce <simo@redhat.com>