Allow excluding tests from certain files

There are certain scripts (such as the ramdisk init script) that
need to ignore linting rules for one reason or another.  This adds
support for exclusions via a comment in the file like:

"# dib-lint: disable=executable sete"

There should be no ", but I need those to prevent git from treating
that as a comment.  This syntax is similar to the pylint exclusion
mechanism.

Exclusion support is added to the executable check, but not
the alphabetical ordering one because I can't imagine a reason we
would need to disable that, and I don't know that comments are
supported in those files anyway.

Change-Id: I9ecfb47269841dc75a005855455ac26ad2cbc642