tox: Stop overriding the 'install_command'

This is not encouraged by infra (particularly mordred and smcginnis)
since it's less obvious and easy to miss.

Change-Id: Ieb4ab13cf8ca5683fcd7b18ed669e8a26659bff1
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

tox.ini

@@ -15,7 +15,6 @@ whitelist_externals =
   rm
   env
   make
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
 setenv =
   VIRTUAL_ENV={envdir}
   LANGUAGE=en_US
@@ -26,7 +25,9 @@ setenv =
   PYTHONDONTWRITEBYTECODE=1
 # TODO(stephenfin): Remove psycopg2 when minimum constraints is bumped to 2.8
   PYTHONWARNINGS = ignore::UserWarning:psycopg2
-deps = -r{toxinidir}/test-requirements.txt
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/test-requirements.txt
 passenv =
   OS_DEBUG GENERATE_HASHES
 # there is also secret magic in subunit-trace which lets you run in a fail only
@@ -76,7 +77,7 @@ setenv = {[testenv]setenv}
 # here instead of test-requirements because we do not want placement present
 # during unit tests.
 deps =
-  -r{toxinidir}/test-requirements.txt
+  {[testenv]deps}
   git+https://opendev.org/openstack/placement#egg=openstack-placement
 commands =
 # NOTE(cdent): The group_regex describes how stestr will group tests into the
@@ -150,8 +151,7 @@ commands =
 
 [testenv:venv]
 deps =
-  -r{toxinidir}/requirements.txt
-  -r{toxinidir}/test-requirements.txt
+  {[testenv]deps}
   -r{toxinidir}/doc/requirements.txt
 commands =
   {posargs}
@@ -159,7 +159,9 @@ commands =
 [testenv:docs]
 description =
   Build main documentation.
-deps = -r{toxinidir}/doc/requirements.txt
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/doc/requirements.txt
 commands =
   rm -rf doc/build/html doc/build/doctrees
   # Check that all JSON files don't have \r\n in line.
@@ -211,7 +213,7 @@ commands =
 description =
   Build all documentation including API guides and refs.
 envdir = {toxworkdir}/docs
-deps = -r{toxinidir}/doc/requirements.txt
+deps = {[testenv:docs]deps}
 commands =
   {[testenv:docs]commands}
   {[testenv:api-guide]commands}
@@ -261,19 +263,14 @@ import_exceptions = nova.i18n
 # system dependencies are missing, since it's used to tell you what system
 # dependencies are missing! This also means that bindep must be installed
 # separately, outside of the requirements files, and develop mode disabled
-# explicitly to avoid unnecessarily installing the checked-out repo too (this
-# further relies on "tox.skipsdist = True" above).
+# explicitly to avoid unnecessarily installing the checked-out repo too
 usedevelop = False
 deps = bindep
 commands =
   bindep test
 
 [testenv:lower-constraints]
-# We need our own install command to avoid upper constraints being considered
-# when making the environment. Set usedevelop to false to avoid pbr installing
-# requirements for us so all requirements are installed in one call to pip.
 usedevelop = False
-install_command = pip install {opts} {packages}
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt