[feat] Change default JSON report file pattern

[jgphpc]

Will fix #1476

[codecov-commenter]

Codecov Report

Merging #1480 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1480   +/-   ##
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  Coverage   91.72%   91.72%           
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  Files          82       82           
  Lines       12924    12924           
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  Hits        11854    11854           
  Misses       1070     1070           

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[vkarak]

One thing that's not very nice is that the configuration option must be enabled in order for the --report-file command-line option to have an effect, which is a bit strange. As a user I would expect to get a report if I pass that option. One solution could be to automatically enable reporting if this option is passed. The downside of this is that it will break somehow the consistency of command line options mapping to configuration options. Another decision to make is what should be the default behaviour: generate or not the report. I kind of tend to not generate, but I'm not sure. This decision will also guide us to what would be the best solution to the problem I just described.

Apart from this, we will need to update the documentation.

[jgphpc]

Tested with:

• pytest-3 unittests/test_cli.py
• reframe hello1.py -> ~/.reframe/reports/run-report.json
• reframe --report-file=/tmp/0_{sessionid}.json -r -c hello1.py -> /tmp/0_0.json
• reframe --mode maintenance -C cscs.py -r -c hello1.py -> $APPS/.../run-report-0.json
• RFM_REPORT_FILE=/tmp/0.json reframe -r -c hello1.py -> /tmp/0.json

[vkarak]

lgtm now