Fix lower-constraint deps handling

When the lower-constraints tox target was added, it was assumed the
install_command was just running the install and that the dependencies
and constraints were being set using "deps = ".

This fixed the install_command and deps to follow the expected pattern
so the lower-constraints job actual does install the lower constraints.

Change-Id: I5e2eceeb874ccde90bac1a6345fcce713db1d056
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

tox.ini

@@ -5,7 +5,7 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
+install_command = pip install {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
          OS_STDOUT_CAPTURE=1
          OS_STDERR_CAPTURE=1
@@ -13,8 +13,10 @@ setenv = VIRTUAL_ENV={envdir}
          OS_TEST_PATH=./brick_cinderclient_ext/tests/unit
 passenv = *_proxy *_PROXY
 
-deps = -r{toxinidir}/requirements.txt
-       -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 =
            find . -type f -name "*.pyc" -delete
            stestr run {posargs}