* Set validation-sets on actions when refreshing and assembling actual JSON.
There was a bug where validation-sets were set on actions when
refreshing, but when actual snap actions were transformed into JSON
request the validation-sets field would only get carried over for
"install".
* Also support passing validation-sets in current snap context.
* Set validation-sets unconditionally on action json (it's going to be
nil except for install/refresh).