Fixes for tox 4.0

- Fixed passenv syntax
- Removed usedevelop (not allowed with skipsdist)

Change-Id: I2279b81c8d9975300be9d0bd8c035963021ce6df

tox.ini

@@ -6,7 +6,6 @@ ignore_basepython_conflict=true
 
 [testenv]
 basepython = python3
-usedevelop = True
 setenv =
     VIRTUAL_ENV={envdir}
     PYTHONWARNINGS=default::DeprecationWarning
@@ -15,10 +14,15 @@ deps =
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/test-requirements.txt
 commands = stestr run --slowest {posargs}
-passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
+passenv =
+    http_proxy
+    HTTP_PROXY
+    https_proxy
+    HTTPS_PROXY
+    no_proxy
+    NO_PROXY
 
 [testenv:pep8]
-usedevelop = False
 deps =
     Pygments>=2.2.0 # BSD license
     doc8>=0.8.1 # Apache-2.0
@@ -36,14 +40,12 @@ commands = {posargs}
 commands = python setup.py test --coverage --testr-args='{posargs}'
 
 [testenv:docs]
-usedevelop = False
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
-usedevelop = False
 allowlist_externals = make
 deps = {[testenv:docs]deps}
 commands =
@@ -54,7 +56,6 @@ commands =
 commands = oslo_debug_helper -t bifrost/tests {posargs}
 
 [testenv:releasenotes]
-usedevelop = False
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
@@ -77,7 +78,6 @@ application-import-names = bifrost
 filename = *.py
 
 [testenv:linters]
-usedevelop = False
 allowlist_externals = bash
 deps =
   ansible>=5,<6