testlib: Count passes, fails and skips consistently.

testlib: Count passes, fails and skips consistently.

For data-driven tests, testlib previously counted one fail or skip for
each data row that failed or skipped, while it counted only one pass
for a test function where all rows passed and counted no passes for a
test function where some rows passed and some rows failed. A similar
problem also existed for benchmark tests, which could run multiple
iterations of the same test, with each fail and skip being counted but
only a single pass being counted for the entire series of iterations.

This commit makes testlib count one pass, fail or skip for each data
row.  Test functions that are not data-driven count one result for the
test function, as before.  Benchmark tests count one pass, fail or skip
per iteration.

A side-effect of this change is that the test output in plain text, xml
and light xml formats now shows a result for every data row and
benchmark iteration executed, allowing post-processors to correctly
calculate the total number of tests executed.  Previously, individual
rows were not shown in the test output if they passed, making such
calculations impossible.

The only change to the xunitxml output format is to correct a bug where
no test result was recorded for a test function if the last data row
was skipped and all other rows passed -- in which case the overall
result should be a pass.  Note that there is also a pre-existing bug
in the xunit logger, where no result is reported if all rows are
skipped; that bug is unaffected by this commit.

Task-number: QTBUG-21848
Task-number: QTBUG-22124
Change-Id: I7e17177e10d6e89e55b9684c159bd506f21d002b
Reviewed-by: Ed Baak <ed.baak@nokia.com>