Enable API GET filtering against Array values

Users are unable to filter against values such as 'tags' or 'hw_id' because a regex can not be applied to array values. This fix converts array values to a comma separated string and assigns it to a local variable. The regex is applied to this local variable. See issue #489.

This fix was tested against the node and active_model slices using the following commands:

wget -qO- .../razor/api/node?hw_id=regex:0025B500004D | jq '.'

wget -qO- .../razor/api/active_model?tags=regex:MYTAG | jq '.'