tripleo scripts should be kept as portable as possible

[Sorin Sbarnea]

Bash scripts used by tripleo like quickstart.sh or reproducer.sh should limit their use of new bash syntax and keep using old but portable ways, which work on most platforms.

Example of less portable code:
* &>> is bash4 only, use old 2>&1 >> instead.
* avoid using `-v VAR` to test if a variable exists, use old [[ -z "${FOO:-}" ]] - see https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash

BSD tools (non GNU) like bash, sed can have a slightly different option across platform. For example MacOS has a bash version 3.4 even on 10.14. Running reproducer from a BSD machine should be possible as long deployment takes place on a remote VIRSHOST or an openstack cloud.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Sorin Sbarnea (<email address hidden>) on branch: master
Review: https://review.openstack.org/581012
Reason: life-too-short to chaise this one