log improvement

[segaura]

Hallo.
My suggestion is to improve the logging.
Current problems are:

• Output log level cannot be controller via options, it is hardcoded
• "printd()" method mixes log, output message and has also dependency on it parent implementation, because of the "self.driver != "HPSUD"" check
• Developers are discouraged to add log because of how "printd()" is implemented, the risk of writing to stdout along command output is real; current code has no log at DEBUG or INFO level probably because of this
• Log is substantially absent
• Implemented log levels are not the usual ones, e.g. DEBUG level is missing
• Logging methods specify level using strings and this is prone to error and inhibits code auto-completion

I prepared a pull request solving all of this, it is really "big" because it removes printd() in favor of standard logging methods and this involves almost all of the python files.
I will submit the pull request so we can discuss on the technical decisions, if you are interested on.