Consistently use jsonutils instead of specific implementation

jsonutils have several benefits in comparison to pure json
implementation, like enabling C boosted encoders and decoders for
Python2.6 by using simplejson when available.

Change-Id: I24d0cd442e8d9d89fac50e43fc97f7bb4a293c3d
Closes-Bug: 1329496
Merge "Consistently use jsonutils instead of specific implementation"