jenkins: ctest output size for failed test is too shot
We observe sporadic failures for rbd-mirror  and librbd  unit tests for jenkins make check. The problem is that the test's output buffer is too short and we don't see which test exactly fails to nail it down (trying to reproduce it locally rerunning the whole test set has not succeeded so far).
Can we increase somehow the output size? I suppose it can be tweaked by `--test-output-size-failed` ctest option . Also, there is the cmake variable `CTEST_CUSTOM_MAXIMUM_FAILED_TEST_OUTPUT_SIZE` , which according to the documentation is 300K.
Interestingly, the amd64 jenkins shows the whole fail test output, though I failed to find any related difference in ceph-build scripts between x86 and amd64. Probably, ctest is built with different default values there.
The easiest way to see the problem, I think, is to add something like `exit 1` at the end of `src/test/run-rbd-unit-tests.sh` to make it fail.