3.0 fails with importorskip on module level

[The-Compiler]

Because 3.0 disallows pytest.skip at module-level, using pytest.importorskip fails:

import pytest
foobarbaz = pytest.importorskip("foobarbaz")

def test_foo():
    pass

with 2.9.2:

========================== test session starts ===========================
platform linux -- Python 3.5.2, pytest-2.9.2, py-1.4.31, pluggy-0.3.1
rootdir: /home/florian, inifile: 
plugins: mock-1.2
collected 0 items / 1 skipped 

with 3.0.0:

========================== test session starts ===========================
platform linux -- Python 3.5.2, pytest-3.0.0, py-1.4.31, pluggy-0.3.1
rootdir: /home/florian, inifile: 
plugins: hypothesis-2.0.0, catchlog-1.2.1
collected 0 items / 1 errors 

================================= ERRORS =================================
_________________________ ERROR collecting x.py __________________________
Using @pytest.skip outside a test (e.g. as a test function decorator) is not allowed. Use @pytest.mark.skip or @pytest.mark.skipif instead.
!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!
======================== 1 error in 0.13 seconds =========================

This was pointed out in #pylib by @jaraco as setuptools did run into it: test_msvc.py

I think this is a valid pattern (and the error message is confusing) - maybe pytest.skip should have some allow_module_level argument and importorskip should use it (without me actually having looked at the code)?

cc @omarkohl

[nicoddemus]

Probably what's happening is that importorskip uses pytest.skip directly... without looking at the code I think the easiest solution is for importorskip to raise SkipError (or something) directly instead.

[nicoddemus]

@The-Compiler went with your suggestion, going to open a PR in a few minutes.