Add MiqReportResult#contains_records?

https://bugzilla.redhat.com/show_bug.cgi?id=1590908

Like `MiqReportResult#has_report?`, this is a faster version of checking
if the report_result has rows.

Like `MiqReport#contains_records?`, this will check against the `extras`
attribute on the deserialized version of the `report` column, but
instead of using the `table` value (which is not saved into the `report`
column), just do a light SQL existence check on the `html_details` to
confirm there are generated rows for this report.

The SQL query most likely won't be needed, and it is super light weight,
only returning a single digit, or an empty result set if there are no
records.

app/models/miq_report_result.rb

@@ -60,6 +60,13 @@ def valid_report_column?
     report.kind_of?(MiqReport)
   end
 
+  # Use this over `report_results.contains_records?` if you don't need to
+  # access the binary_blob associated with the MiqReportResult (chances are you
+  # don't need it)
+  def contains_records?
+    (report && (report.extras || {})[:total_html_rows].positive?) || html_details.exists?
+  end
+
   def report_results
     if binary_blob
       data = binary_blob.data