Fix get_count_total(). Accept -1 value set by the server.

[jjnicola]

What:

The value set by the server has priority over the value
calculated from the original target list by ospd.
As ospd is not intelligent enough to check the amount of valid
hosts, check for duplicated or invalid hosts, consider a negative
value set for the server, in case it detects an invalid target string
or a different amount than the orignal amount in the target list.

Why:
Let ospd to set a scan with an invalid target as finished instead of interrupted, but there is no other result than the error message to inform the client about the invalid target.

How:

• Set debug log level in ospd.
• Start a scan with an invalid target list (only possible via gvm-cli, as gsa wont you to create a invalid target).
• check with <get_scans> that the scan results xml element has "status = finished" and "progress=100"
• check that the only result is the error message.

$ gvm-cli --protocol OSP --timeout 120 socket --socketpath=/home/jnicola/install/var/run/ospd/openvas.sock --xml "<get_scans scan_id='829097a9-85d5-4bb8-bac0-e64c362b2836'/>"|xmlstarlet fo
<?xml version="1.0"?>
<get_scans_response status="200" status_text="OK">
  <scan end_time="1611925139" id="829097a9-85d5-4bb8-bac0-e64c362b2836" progress="100" start_time="1611925136" status="finished" target="some$invalid.target.net.%com">
    <results>
      <result host="" hostname="" name="" port=" " qod="" severity="" test_id="" type="Error Message" uri="">Invalid target list: some$invalid.target.net.%com.</result>
    </results>
  </scan>
</get_scans_response>

Checklist:

• Tests
• CHANGELOG Entry

[jjnicola]

Depends on PR greenbone/openvas-scanner#646

[codecov]

Codecov Report

Merging #355 (c88399c) into ospd-20.08 (98ebda9) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           ospd-20.08     #355      +/-   ##
==============================================
+ Coverage       73.91%   73.93%   +0.02%     
==============================================
  Files              23       23              
  Lines            2603     2605       +2     
==============================================
+ Hits             1924     1926       +2     
  Misses            679      679              

Impacted Files	Coverage Δ
ospd/scan.py	92.62% <100.00%> (+0.06%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 98ebda9...c88399c. Read the comment docs.