Revert "refs #4119 - hammer-manifest - do not convert params to_json since this prevents passing File objects to POST"

This reverts commit c73496a2aba3585d6abd78a6c2be47e8f7bc0439.

this is undoing the commit that breaks Katello's wrap_parameters
Merge pull request #24 from komidore64/tom-breaking-stuff

Revert "refs #4119 - hammer-manifest - do not convert params to_json since this prevents passing File objects to POST"