Faster get_attrname in nova/objects/base.py

get_attrname function is called very very often,
and it's string concatenation method is not fast.

* Changing the string concatenation to a 2 times
  faster + operator instead of the % operator.

Change-Id: I326fd6dda8dd41a90757c69867afd62063231362
Error code for creating secgroup default rule

Trying to create secgroup group default rules
that already exists gives HttpBadRequest error,
but it should raise HttpConflict.

So updated the code to HttpConflict error.
Closes-Bug: #1374320

Change-Id: I93c6eb7fb96e7109404206367ed81495a4724296
Merge "Error code for creating secgroup default rule"
Merge "Faster get_attrname in nova/objects/base.py"