Always set end_time for interrupted scans.

[jjnicola]

What:
Always set end_time for interrupted scans.

Why:
end-time was set via set_scan_status (stopped). Now, the scan can be interrupted directly and the end time will be set.

How:
Interrupt a running scan and check with <get_scans="SCAN-ID"/>that the end_time is set.

Checklist:

• Tests
• CHANGELOG Entry

[codecov]

Codecov Report

Merging #353 (2c2c47d) into ospd-20.08 (12cda0d) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           ospd-20.08     #353      +/-   ##
==============================================
- Coverage       73.91%   73.90%   -0.02%     
==============================================
  Files              23       23              
  Lines            2603     2602       -1     
==============================================
- Hits             1924     1923       -1     
  Misses            679      679              

Impacted Files	Coverage Δ
ospd/ospd.py	71.64% <ø> (-0.05%)	⬇️
ospd/scan.py	92.53% <100.00%> (ø)

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