Make reports with python-subunit>=1.4

This also speedup tox env creation of 'report' and 'bindep'
by skipping tox installation step.

Change-Id: I76c720012ecb7e81a519c61c583ae0c73788d655

report-requirements.txt

@@ -1,5 +1,7 @@
 # Requirements file for 'report' Tox environment
 
-os-testr>=1.0   # Apache-2.0
-stestr>=2.0     # Apache-2.0
 junitxml>=0.7                                  # LGPL-3
+os-testr>=1.0                                  # Apache-2.0
+python-subunit>=1.4 ; python_version >= '3.0'  # Apache-2.0
+python-subunit<1.4 ; python_version < '3.0'    # Apache-2.0
+stestr>=2.0                                    # Apache-2.0

tox.ini

@@ -251,14 +251,13 @@ commands =
 [testenv:report]
 
 basepython = {env:PYTHON:python3}
-skipsdist=True
-usedevelop = False
+usedevelop = false
+skipdist = true
+skip_install = true
 deps = -r {toxinidir}/report-requirements.txt
 passenv = {[base]passenv}
 setenv = {[base]setenv}
-commands =
-    pip install git+https://github.com/testing-cabal/subunit.git@master
-    {toxinidir}/tools/ci/make_report
+commands = {toxinidir}/tools/ci/make_report
 
 
 [testenv:bindep]
@@ -267,5 +266,8 @@ basepython = {env:PYTHON:python3}
 # 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.
+usedevelop = false
+skipdist = true
+skip_install = true
 deps = bindep
 commands = bindep {posargs:test}