Disable auto-discovery for setuptools

With setuptools release 61.0.0 sahara-image-elements' package build
command (python3 setup.py sdist bdist_wheel) started to fail:

error: Multiple top-level packages discovered in a flat-layout:
['roles', 'elements', 'playbooks'].

This bug is mentioned in setuptools issue 3197 [1], and the suggested
workaround is to disable auto-discovery by adding 'py_modules=[]' in
setup.py.

To unblock the gate the following needed to be updated as well:
- requirements constraints
- fix lower-constraints job constraints (only the 1st constraints is
  used by pip, which was upper-constraints.txt from install command)

[1] https://github.com/pypa/setuptools/issues/3197

changes:
  tox.ini

NOTE(elod.illes): upper constraints should point to yoga version of the
file in stable/yoga.

Change-Id: Ib2d3e296e6d405671594dfd630e381ae414a2709
(cherry picked from commit 008b0d7e83)

lower-constraints.txt

@@ -1,15 +1,15 @@
 Babel==2.5.3
-bashate==0.5.1
+bashate==2.1.0
 decorator==4.2.1
-dib-utils==0.0.11
-diskimage-builder==2.11.0
-flake8==2.5.5
-hacking==0.12.0
-mccabe==0.2.1
+dib-utils==0.0.8
+diskimage-builder==1.1.2
+flake8==3.6.0
+hacking==3.0.1
+mccabe==0.6.0
 networkx==1.11
-pbr==3.1.1
+pbr==2.0.0
 pep8==1.5.7
-pyflakes==0.8.1
+pyflakes==2.0.0
 pytz==2018.3
 PyYAML==3.12
 six==1.11.0

setup.py

@@ -17,4 +17,5 @@ import setuptools
 
 setuptools.setup(
     setup_requires=['pbr>=2.0.0'],
-    pbr=True)
+    pbr=True,
+    py_modules=[])

test-requirements.txt

@@ -2,5 +2,5 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
-bashate>=0.5.1 # Apache-2.0
-hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
+bashate>=2.1.0 # Apache-2.0
+hacking>=3.0.1,<3.1.0 # Apache-2.0

tox.ini

@@ -6,10 +6,10 @@ skipsdist = True
 [testenv]
 basepython = python3
 usedevelop = True
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
 setenv =
     VIRTUAL_ENV={envdir}
 deps =
+    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/yoga}
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/test-requirements.txt
 passenv = http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY