Make the lookup of vcf result more specific

This should aleviate some situations that previously lead to failures:

1) When the parameters to a detector/filter change, downstream
shortcut attempts could find multiple vcf results.

2) When a test-name was set on a detector result or the vcf result,
downstream shortcut attempts could find multiple vcf results.

Now, the get_vcf_result method will do a get_with_lock for filters and
combine results which requires that all params and inputs be specified.