on ubuntu bionic grenade has incorrect python 3 version

[Tom Barron]

If we run grenade with ubuntu bionic nodeset it tries to use python 3.5 even though the python 3 version in bionic is 3.6. Here is the grenade.sh log from a test review [1].

2019-01-17 11:39:06.078 |
2019-01-17 11:39:06.078 | #********************************************
2019-01-17 11:39:06.078 | # grenade.sh log /opt/stack/logs/grenade.sh.log.2019-01-17-113906
2019-01-17 11:39:06.078 | #********************************************
2019-01-17 11:39:06.078 |
2019-01-17 11:39:06.078 | + fetch_devstacks
2019-01-17 11:39:06.078 | + [[ ! -d /opt/stack/old/devstack ]]
2019-01-17 11:39:06.078 | + [[ ! -d /opt/stack/new/devstack ]]
2019-01-17 11:39:06.078 | + source /opt/stack/new/devstack/functions-common
2019-01-17 11:39:06.094 | + source /opt/stack/new/devstack/inc/python
2019-01-17 11:39:06.100 | + install_devstack_tools
2019-01-17 11:39:06.100 | + local dstools_version=0.4.0
2019-01-17 11:39:06.100 | + install_python3
2019-01-17 11:39:06.100 | + is_ubuntu
2019-01-17 11:39:06.100 | + [[ -z '' ]]
2019-01-17 11:39:06.100 | + GetOSVersion
2019-01-17 11:39:06.100 | + _ensure_lsb_release
2019-01-17 11:39:06.100 | ++ command -v lsb_release
2019-01-17 11:39:06.101 | + [[ -x /usr/bin/lsb_release ]]
2019-01-17 11:39:06.101 | + return
2019-01-17 11:39:06.101 | ++ lsb_release -r -s
2019-01-17 11:39:06.156 | + os_RELEASE=18.04
2019-01-17 11:39:06.156 | ++ lsb_release -c -s
2019-01-17 11:39:06.210 | + os_CODENAME=bionic
2019-01-17 11:39:06.211 | ++ lsb_release -i -s
2019-01-17 11:39:06.263 | + os_VENDOR=Ubuntu
2019-01-17 11:39:06.263 | + [[ Ubuntu =~ (Debian|Ubuntu|LinuxMint) ]]
2019-01-17 11:39:06.263 | + os_PACKAGE=deb
2019-01-17 11:39:06.263 | + typeset -xr os_VENDOR
2019-01-17 11:39:06.263 | + typeset -xr os_RELEASE
2019-01-17 11:39:06.263 | + typeset -xr os_PACKAGE
2019-01-17 11:39:06.263 | + typeset -xr os_CODENAME
2019-01-17 11:39:06.263 | + '[' deb = deb ']'
2019-01-17 11:39:06.263 | + apt_get install python3.5 python3.5-dev
2019-01-17 11:39:06.276 | + sudo DEBIAN_FRONTEND=noninteractive http_proxy= https_proxy= no_proxy= apt-get --option Dpkg::Options::=--force-confold --assume-yes install python3.5 python3.5-dev
2019-01-17 11:39:06.314 | Reading package lists...
2019-01-17 11:39:06.514 | Building dependency tree...
2019-01-17 11:39:06.514 | Reading state information...
2019-01-17 11:39:06.716 | E: Unable to locate package python3.5-dev
2019-01-17 11:39:06.716 | E: Couldn't find any package by glob 'python3.5-dev'
2019-01-17 11:39:06.716 | E: Couldn't find any package by regex 'python3.5-dev'

[1] https://review.openstack.org/#/c/631472/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/630961
Committed: https://git.openstack.org/cgit/openstack-dev/grenade/commit/?id=d5dc033a2e6df988b0576fc0417be46cc8d157ed
Submitter: Zuul
Branch: master

commit d5dc033a2e6df988b0576fc0417be46cc8d157ed
Author: Tom Barron <email address hidden>
Date: Tue Jan 15 07:43:33 2019 -0500

    Determine PYTHON3_VERSION when necessary

    When grenade.sh is invoked by devstack-gate, PYTHON3_VERSION
    is not set so grenadrc defaults it to 3.5, which breaks grenade
    on nodes where python 3.5 does not exist, such as ubuntu bionic.

    One solution is to set PYTHON3_VERSION in devstack-gate [1].
    Alternatively, this change uses a bit of code borrowed from
    stackrc in devstack to determine the version of python
    within grenade if it was not set by the caller.

    Closes-bug: #1812208
    [1] https://review.openstack.org/#/c/607379/

    Change-Id: I0349de2026c49279ba7f262d5e86d37018d66326

[OpenStack Infra (hudson-openstack)]

Change abandoned by Tom Barron (<email address hidden>) on branch: master
Review: https://review.openstack.org/631472