Speed up GET_VULNS

[mattmundell]

What:

Speed up GET_VULNS:

1. Remove extra time columns that were just doing ISO conversion from the iterator
2. Use EXISTS instead of "count" in the WHERE clause.
3. Also use EXISTS in the counts.

Why:

GET_VULNS is slow with many results.

With my 1.2 million result db:

After 1 the gvmd vuln query went from 25s to 20s.
After 2 the query went down to 6s.

After 1 and 2 the request in GSA that gets the vulns went down from about 60k ms to 21k ms.
After 3 the GSA request went down to 11k ms.

How did you test it:

Open GSA Vulnerabilities page. Check times in network tab and in gvmd logs.

Checklist:

• Tests
• CHANGELOG Entry