Ignore import lines with noqa

flake8 says that lines with '# noqa' should be ignored, but the
import rules checker isn't ignoring those lines.

This change makes it so that import lines with # noqa are ignored.

Change-Id: Icb2c3eaf0cec87e18bc3c6dcf28f8e2642ec23a2
Fixes: bug 1186188
(cherry picked from commit d728031755269d352ea43c1ea4fb59fd0eceebd5)
Merge "Ignore import lines with noqa" into 0.5.x