'integer expression expected' errors on Ubuntu

[iain MacDonnell]

With USE_PYTHON3 on Ubuntu, we get:

.../devstack/inc/python: line 52: [: 16.04: integer expression expected

Apparently the old-style test attempts to evaluate the RHS of the '-a' expression, even if the LHS evaluates to false.

It's somewhat cosmetic (it fails in the right direction), but ugly.

bash-style tests, [[...]], don't have this issue.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/608065

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/608065
Committed: https://git.openstack.org/cgit/openstack-dev/devstack/commit/?id=e991f7da457e0f1343ca13e8adeb0f6334b04990
Submitter: Zuul
Branch: master

commit e991f7da457e0f1343ca13e8adeb0f6334b04990
Author: imacdonn <email address hidden>
Date: Thu Oct 4 19:41:59 2018 +0000

    Use bash-style test for Fedora version

    Old-style test fails on Ubuntu when python3 enabled, with:

    .../devstack/inc/python: line 52: [: 16.04: integer expression expected

    Use bash-style test, which doesn't attempt to evaluate the RHS if the
    LHS evaluates to false

    Change-Id: If18031ab98c9060e5825c3a8d3c647bd3705cd9c
    Closes-Bug: #1796174