Enable Flake8 F*** checks.

Fix and enable F*** Checks by removing unused imports.

Change-Id: I39863a4664abff1349911546f16bfea055104e63

diskimage_builder/elements.py

@@ -14,7 +14,6 @@
 # under the License.
 
 import argparse
-from errno import ENOENT
 import os
 import sys
 

diskimage_builder/test_elementdeps.py

@@ -16,7 +16,7 @@
 import os
 
 from testtools import TestCase
-from fixtures import Fixture, EnvironmentVariable, TempDir
+from fixtures import EnvironmentVariable, TempDir
 
 from diskimage_builder.elements import expand_dependencies
 from diskimage_builder.elements import get_elements_dir

diskimage_builder/test_elements.py

@@ -15,7 +15,6 @@
 
 import os
 import sys
-import unittest
 
 
 class StubPackage:

tox.ini

@@ -40,7 +40,7 @@ commands = bash -c 'if [ ! -d ./.testrepository ] ; then testr init ; fi'
 downloadcache = ~/cache/pip
 
 [flake8]
-ignore = E125,F,H
+ignore = E125,H
 builtins = _
 exclude =  .venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build