Do not invoke update PTG from create PTG

Removed invoking PTG update from within create PTG.
This ends up invoking update api before create postcommit is
invoked on other configured drivers(ML2 model).
The shared resource validation is made while setting the context

Change-Id: I9b08b44f6fbc7de2cc1ebfae05b63992066d6046
Closes-bug: #1403471
Merge "Do not invoke update PTG from create PTG"