Leverage dict comprehension in PEP-0274

Leverage dict comprehension in PEP-0274

PEP-0274 introduced dict comprehensions to replace dict constructor
with a sqeuence of key-pairs[1], these are benefits:
  First, it makes the code look neater.
  Second, it gains a micro-optimization.

Cinder dropped python 2.6 support in Kilo, we can leverage this now.
Note: This commit doesn't handle dict constructor with kwargs.
This commit also adds a hacking rule.

[1]http://legacy.python.org/dev/peps/pep-0274/

Change-Id: Ie65796438160b1aa1f47c8519fb9943e81bff3e9