Sync tools/tox_install.sh
Sync tools/tox_install.sh

Sync tools/tox_install.sh with python-openstackclient. This brings in
the following improvements:

* Do not leave temporary directory around, instead delete temporary
  directory directly after usage (change
  I939eae82dba3287fd4e4086128ebf4609a0e0770).
* Do not set ZUUL_BRANCH explicitely and remove unused if condition
  (change I0077c986a17d6bb92791474e03d1e77776e9382f).

Change-Id: I455222311fb1e9e029cb586c8cc6a06debaaa225

openstack/ironic-lib,NaohiroTamura/ironic-lib