Pin networkx in constraints (Qiskit#3276)

With the recent release of networkx 2.4 several deprecated APIs were
removed. This broke the visualization dependency nxpd. A fix is in
progress [1] to address this. But in the meantime to get tests working
again we need to make sure we do not install networkx 2.4 for testing.
This commit does this by pinning the version we use in our testing in
the constraints file to 2.3. This will unblock our development while we
wait for a new nxpd release.

[1] chebee7i/nxpd#15

.travis.yml

@@ -32,9 +32,9 @@ cache: pip
 stage_generic: &stage_generic
   install:
     # Install step for jobs that require compilation and qa.
-    - pip install -U -r requirements.txt
+    - pip install -U -r requirements.txt -c constraints.txt
     - pip install -U -r requirements-dev.txt coveralls -c constraints.txt
-    - pip install -e .
+    - pip install -c constraints.txt -e .
     - pip install "qiskit-ibmq-provider" -c constraints.txt
   script:
     # Compile the executables and run the tests.

azure-pipelines.yml

@@ -130,7 +130,7 @@ stages:
             set -e
             python -m pip install --upgrade pip
             pip install -U -r requirements.txt -r requirements-dev.txt -c constraints.txt
-            pip install -e .
+            pip install -c constraints.txt -e .
             pip install "qiskit-ibmq-provider" -c constraints.txt
             python setup.py build_ext --inplace
           displayName: 'Install dependencies'
@@ -180,7 +180,7 @@ stages:
             set -e
             python -m pip install --upgrade pip
             pip install -U -r requirements.txt -r requirements-dev.txt -c constraints.txt
-            pip install -e .
+            pip install -c constraints.txt -e .
             pip install "qiskit-ibmq-provider" -c constraints.txt
             python setup.py build_ext --inplace
           displayName: 'Install dependencies'
@@ -233,7 +233,7 @@ stages:
             set -e
             python -m pip install --upgrade pip
             pip install -U -r requirements.txt -r requirements-dev.txt -c constraints.txt
-            pip install -e .
+            pip install -c constraints.txt -e .
             pip install "qiskit-ibmq-provider" -c constraints.txt
             python setup.py build_ext --inplace
           displayName: 'Install dependencies'
@@ -290,7 +290,7 @@ stages:
             set -e
             python -m pip install --upgrade pip
             pip install -U -r requirements.txt -r requirements-dev.txt -c constraints.txt
-            pip install -e .
+            pip install -c constraints.txt -e .
             pip install "qiskit-ibmq-provider" -c constraints.txt
             python setup.py build_ext --inplace
           displayName: 'Install dependencies'
@@ -342,7 +342,7 @@ stages:
             set -e
             python -m pip install --upgrade pip
             pip install -U -r requirements.txt -r requirements-dev.txt -c constraints.txt
-            pip install -e .
+            pip install -c constraints.txt -e .
             pip install "qiskit-ibmq-provider" -c constraints.txt
             python setup.py build_ext --inplace
           displayName: 'Install dependencies'
@@ -394,7 +394,7 @@ stages:
             set -e
             python -m pip install --upgrade pip
             pip install -U -r requirements.txt -r requirements-dev.txt -c constraints.txt
-            pip install -e .
+            pip install -c constraints.txt -e .
             pip install "qiskit-ibmq-provider" -c constraints.txt
             python setup.py build_ext --inplace
           displayName: 'Install dependencies'

constraints.txt

@@ -1,3 +1,4 @@
 astroid==2.2.5
 cryptography==2.5.0
 pylint==2.3.1
+networkx==2.3