Moved exceptions.py and utils.py up to plugins dir

Plugins dir contains 'general' module which looks like yet another
plugin along with vanilla, fake, hdp, spark and cdh. But it doesn't
and contains two files only. Moved them one level up to avoid such
confusion.

Closes-Bug: #1378178

Change-Id: Ia600e4c584d48a3227552f0051cc3bf906206bed
Merge "Moved exceptions.py and utils.py up to plugins dir"