Remove pytest-catchlog from dependences.

[zenhack]

We've been getting warnings about it having been merged into pytest
core, e.g:

https://travis-ci.org/CCI-MOC/hil/jobs/341455006#L2725

This also bumps the minimum version for pytest in our setup.py, since
the change was made in 3.3.0:

• https://docs.pytest.org/en/latest/changelog.html#id56
• Merge pytest-catchlog plugin pytest-dev/pytest#2794

[naved001]

I tried doing this in #927 and when I removed pytest-catchlog from the requirements, it suddenly couldn't import it. So don't know what's up with that.

From my description there:

One message that is still annoying is this:

=============================================================================================== warnings summary ===============================================================================================
None
  pytest-catchlog plugin has been merged into the core, please remove it from your requirements.

-- Docs: http://doc.pytest.org/en/latest/warnings.html

I removed pytest-catchlog from the requirements, but then I couldn't import pytest_catchlog. Their docs don't say anything about it being merged into the core, it still tells you to install it explicitly. Don't know what's up with that.

[zenhack]

@naved001, found the problem, see the last commit. D'oh.

[xuhang57]

lgtm