neverallow: domain:file execute and entrypoint

Occasionally, files get labeled with the domain type rather
than the executable file type. This can work if the author
uses domain_auto_trans() versus init_daemon_domain(). This
will cause a lot of issues and is typically not what the
author intended.

Another case where exec on domain type might occur, is if
someone attempts to execute a /proc/pid file, this also
does not make sense.

To prevent this, we add a neverallow.

Change-Id: I39aff58c8f5a2f17bafcd2be33ed387199963b5f
Signed-off-by: William Roberts <william.c.roberts@intel.com>