tests: implement coverage reporting

  - move the logic of uploading to WebDAV server here instead of the
 generated bin/runUnitTest wrapper
  - run a new `coverage_report` which will
    - download all coverage data from WebDAV server
    - combine the data
    - run html report, saved in log folder
    - print text output in the text output.

This `coverage_report` test waits for other tests to finish uploading
data, we could extend test node distributor to distribute this test at
the end.
17 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

02:08:57

failed ERP5.PerformanceTest-Master

00:34:38

passed ERP5.UnitTest-Master

03:51:16

passed SlapOS.Eggs.UnitTest-Master.Python2

00:29:36

passed SlapOS.Eggs.UnitTest-Master.Python3

00:29:36

passed Wendelin.UnitTest-Master

01:37:52

failed ERP5.CodingStyleTest-Master

02:17:49

passed ERP5.PerformanceTest-Master

00:34:35

passed SlapOS.Eggs.UnitTest-Master.Python2

00:30:15

passed SlapOS.Eggs.UnitTest-Master.Python3

00:31:05

failed Wendelin.UnitTest-Master

00:02:49

failed Wendelin.UnitTest-Master

00:03:00

failed Wendelin.UnitTest-Master

01:02:42

failed Wendelin.UnitTest-Master

00:03:17

failed Wendelin.UnitTest-Master

00:03:07

failed Wendelin.UnitTest-Master

00:03:18

failed Wendelin.UnitTest-Master

00:02:59