Upgrader, check status code before body pasring in mcollective checker

Sometimes mcollective returns string which
is correct json, as result when we
iterate over this string we get an error
beacuse we expected list of dicts.

blueprint upgrade-to-5-0-1

Closes-bug: #1337337

Change-Id: I8d3f608df7591dcabc36f8e69bcc368d3babbf8a
Merge "Upgrader, check status code before body pasring in mcollective checker" into stable/5.0