PySimLogger: move cmd2 import to where it is needed

The PySimLogger has a dependency to cmd2, however this dependency is
only required in one specific corner case. We can move the import
to the related code section and remove the dependency for all other
cases.

Change-Id: Idfdfcd27eef8d87bea75230600c7be1e7a8ba749
Related: SYS#6959

pySim/log.py

@@ -24,7 +24,6 @@
 #
 
 import logging
-from cmd2 import style
 
 class _PySimLogHandler(logging.Handler):
     def __init__(self, log_callback):
@@ -121,6 +120,7 @@ class PySimLogger:
                 if isinstance(color, str):
                     PySimLogger.print_callback(color + formatted_message + "\033[0m")
                 else:
+                    from cmd2 import style
                     PySimLogger.print_callback(style(formatted_message, fg = color))
             else:
                 PySimLogger.print_callback(formatted_message)