1006748: replace simplejson with 'ourjson'

ourjson is just a compability wrapper.
It will use simplejson if installed, our the
builtin python json if simplejson is not installed.

On RHEL6, simplejson is much faster than the builtin
json module. This lets us choose which dep we want
from the rpm spec.
Removed python-simplejson from the spec file
Merge pull request #95 from candlepin/alikins/1006748_ourjson

Alikins/1006748 ourjson