don't use FileExistsError in mkdir function (doesn't exist in Python 2.7)

[Flamefire]

Follow-up to #4300 which introduced a Python3 class

Fix by introducing a Python2 implementation and using that.

[boegel]

lgtm

[boegel]

@Flamefire Hmm, new test fails:

Traceback (most recent call last):
  File "/tmp/runner/e377429f58b1fec22562d603da05e3480ca0cfff/lib/python3.6/site-packages/test/framework/filetools.py", line 3399, in test_compat_makedirs
    self.assertErrorRegex(Exception, os.path.basename(name), py2vs3.makedirs, name)
  File "/tmp/runner/e377429f58b1fec22562d603da05e3480ca0cfff/lib/python3.6/site-packages/easybuild/base/testing.py", line 178, in assertErrorRegex
    self.assertTrue(regex.search(msg), "Pattern '%s' is found in '%s'" % (regex.pattern, msg))
AssertionError: None is not true : Pattern 'folder' is found in '17'

edit: fixed in 40f9fe7

[boegel]

We overlooked this because we stopped running the tests on top of Python 2 in #4267, ugh...

ERROR: test_mkdir (__main__.FileToolsTest)
Test mkdir function.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/arcanine/scratch/gent/vo/000/gvo00002/vsc40023/easybuild/easybuild-framework/test/framework/filetools.py", line 631, in test_mkdir
    check_mkdir(barfoodir, error="Failed.*No such file or directory")
  File "/arcanine/scratch/gent/vo/000/gvo00002/vsc40023/easybuild/easybuild-framework/test/framework/filetools.py", line 623, in check_mkdir
    self.assertErrorRegex(EasyBuildError, error, ft.mkdir, path, **kwargs)
  File "easybuild/base/testing.py", line 170, in assertErrorRegex
    call(*args, **kwargs)
  File "easybuild/tools/filetools.py", line 1924, in mkdir
    except FileExistsError as err:
NameError: global name 'FileExistsError' is not defined

[Flamefire]

@Flamefire Hmm, new test fails:

Traceback (most recent call last):
  File "/tmp/runner/e377429f58b1fec22562d603da05e3480ca0cfff/lib/python3.6/site-packages/test/framework/filetools.py", line 3399, in test_compat_makedirs
    self.assertErrorRegex(Exception, os.path.basename(name), py2vs3.makedirs, name)
  File "/tmp/runner/e377429f58b1fec22562d603da05e3480ca0cfff/lib/python3.6/site-packages/easybuild/base/testing.py", line 178, in assertErrorRegex
    self.assertTrue(regex.search(msg), "Pattern '%s' is found in '%s'" % (regex.pattern, msg))
AssertionError: None is not true : Pattern 'folder' is found in '17'

edit: fixed in 40f9fe7

Your fix works, thanks! For reference: "17" is EEXISTS, strange that the name isn't always included.

[boegel]

I've opened #4333 to bring back running the test suite with Python 2.7...