diskimage-builder fails pep8 because file cannot detect use of dib-python as python script

[Darragh Bailey]

Running 'tox -e pep8' locally for diskimage-builder fails with the following in the output:

ERROR: elements/package-installs/bin/package-installs-v2 should use 4 spaces indent
45: " 'install.d' or pre-install.d")
48: " packages to install are shown")

This occurs because when 'file' is used to get the mime-type of elements/package-installs/bin/package-installs-v2, it returns 'text/plain' instead of python as the first line of the script is '#!/usr/local/bin/dib-python', resulting in the custom bash orientated style checking instead of using flake8.

Tested on Ubuntu 16.04

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/321126

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/321126
Committed: https://git.openstack.org/cgit/openstack/diskimage-builder/commit/?id=716be1d6f0d8fe26c0a1b294cdb8228596e4aedc
Submitter: Jenkins
Branch: master

commit 716be1d6f0d8fe26c0a1b294cdb8228596e4aedc
Author: Darragh Bailey <email address hidden>
Date: Wed May 25 16:49:59 2016 +0100

    Handle file magic type varying order matching

    Allow file test to return all possible mime-types and ensure anything
    that matches the python file type is parsed by flake8 instead of
    relying on the first match returned.

    Closes-Bug: #1585688
    Change-Id: Iba31f1853537fe9234ab6f83d66f13dc1c578abb