1006748: replace simplejson with 'ourjson'

ourjson is just a compability wrapper from python-rhsm
1.10.3 or higher. 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.
Merge pull request #796 from candlepin/alikins/1006748_ourjson

1006748: replace simplejson with 'ourjson'