Added spec to prove user_plugins failure to update, per #2580
Issue #2580

Changed user_params to permit an array of plugins. Without this, user plugin access was not being persisted.
Remove httparty from test from 3277e67e8afb039500683f414b2df98e5e176fe9

This closes #2555
This closes #2552
Hybrid positive/negative assertion to prove image's presence