Expose --markers option in test_setup.py

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Add pytest.ini to define custom markers

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Deprecate fs_suite pytest marker

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Deprecate pytest cliobj marker

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Add description for long-running pytest marker

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Fix flake8 warning

OME-DCO-1.1-Signed-off-by: Sebastien Besson <seb.besson@gmail.com> (github: sbesson)
Remove unnecessart ptestmark
Merge pull request #2810 from sbesson/rebased/develop/pytest_markers

Pytest markers registration (rebased onto develop)