Avoid tox_install.sh for constraints support

We do not need tox_install.sh, pip can handle constraints itself
and install the project correctly. Thus update tox.ini and remove
the now obsolete tools/tox_install.sh file.

This follows https://review.openstack.org/#/c/508061 to remove
tools/tox_install.sh.

Change-Id: Ie7c06ead39c8597ec9326f223625d1fa0d5208d1

tox.ini

@@ -5,13 +5,15 @@ skipdist = True
 
 [testenv]
 usedevelop = True
-install_command =
-    {toxinidir}/tools/tox_install.sh {env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
+install_command = pip install -U {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
          OS_STDOUT_CAPTURE=1
          OS_STDERR_CAPTURE=1
          OS_TEST_TIMEOUT=60
-deps = -r{toxinidir}/test-requirements.txt
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+  -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/requirements.txt
 commands = ostestr {posargs}
 whitelist_externals = ostestr
 
@@ -54,14 +56,6 @@ commands =
     bandit -r openstackclient -x tests -s B105,B106,B107,B401,B404,B603,B606,B607,B110,B605,B101
 
 [testenv:unit-tips]
-usedevelop = True
-install_command =
-    {toxinidir}/tools/tox_install.sh {env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
-setenv = VIRTUAL_ENV={envdir}
-         OS_STDOUT_CAPTURE=1
-         OS_STDERR_CAPTURE=1
-         OS_TEST_TIMEOUT=60
-deps = -r{toxinidir}/test-requirements.txt
 commands =
     pip install -q -U -e "git+file://{toxinidir}/../cliff#egg=cliff"
     pip install -q -U -e "git+file://{toxinidir}/../keystoneauth#egg=keystoneauth"