BF+TST: Robustify default_result_renderer()

[mih]

Changes:

• avoid spurious whitespace when results carry no path
• prevent crash when path relpath'ing is not possible (fixes Robustify default result renderer #5116)
• make missing action and status declarations more obvious in the
  output (before it was just None)
• add test to verify a bunch of corner cases

Once released with 0.13.6, this could bring piece to the win2019 tests of datalad-osf @adswa

[yarikoptic]

hm, the travis run somehow abruptly ended for _DL_TMPDIR="/var/tmp/sym link" NOSE_SELECTION_OP="" DATALAD_TESTS_OBSCURE_PREFIX=- DATALAD_LOG_TRACEBACK=collide and I do not see even a button to restart it :-/

appveyor is also failing with smth which seems to be unrelated

======================================================================
FAIL: datalad.distribution.tests.test_get.test_get_flexible_source_candidates_for_submodule
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Miniconda35\envs\test-environment\lib\site-packages\nose\case.py", line 198, in runTest
    self.test(*self.arg)
  File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\tests\utils.py", line 750, in _wrap_with_tempfile
    return t(*(arg + (filename,)), **kw)
  File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\tests\utils.py", line 750, in _wrap_with_tempfile
    return t(*(arg + (filename,)), **kw)
  File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\tests\utils.py", line 750, in _wrap_with_tempfile
    return t(*(arg + (filename,)), **kw)
  File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\distribution\tests\test_get.py", line 149, in test_get_flexible_source_candidates_for_submodule
    from_config=True),
AssertionError: [{'cost': 400, 'url': 'youredead', 'from_config': True, 'name': 'bang'}, {'cost': 500, 'url': 'C:\\Users\\appveyor\\AppData\\Local\\Temp\\1\\datalad_temp_5g1v801p\\sub', 'name': 'origin'}, {'cost': 700, 'url': 'pre-60640353-e1d8-4214-9e16-09686627e747-post', 'from_config': True, 'name': 'bang'}] != [{'cost': 500, 'url': 'C:\\Users\\appveyor\\AppData\\Local\\Temp\\1\\datalad_temp_5g1v801p\\sub', 'name': 'origin'}, {'cost': 700, 'url': 'pre-60640353-e1d8-4214-9e16-09686627e747-post', 'from_config': True, 'name': 'bang'}]

overall I do not mind to see this merged, but travis stall is something new to me, so need to be shown that not related

note: we also have @never_fail helper to really make sure a function doesn't raise, but probably would be overkill here

[mih]

overall I do not mind to see this merged, but travis stall is something new to me, so need to be shown that not related

I don't know how to prove that it is not related. But the diff changes the content of a string that is generated. And when rerunning travis, it passed.

[yarikoptic]

reran and passing travis contributes to the proof ;-)