Bump lint jobs to latest stable python version (#3189)

* Bump lint jobs to latest stable python version

The python version used for pylint can effect results returned, pylint
is very sensitive to the environment it's run in. Running on python 3.5
which is the oldest supported python version masks issues on newer
python versions. For example, if you have python 3.7 installed locally
lint will always fail becaues of changes to the stdlib. This starts to
become more of an issue as a particular python version ages, since the
user and contributor base moves to newer versions of python. This commit
changes the version of pylint we run in CI to 3.7 to tests the leading
edge instead of the trailing so we keep our pylint testing up to date
with the python versions we support.

Related to #3127 and #1179

* Add **kwargs to avoid linter error

The abc.ABCMeta class defition added a **kwargs to the __new__ method
definition in python 3.6. This breaks the linter because the
qiskit.pulse.commands.command.MetaCount subclass function signature
differs from stdlib on newer python versions. This works around this by
adding a throwaway kwargs argument to the signature so that we pass
pylint's blind pedantry when running on newer python versions, but still
work with python 3.5.

azure-pipelines.yml

@@ -161,8 +161,8 @@ stages:
       condition: not(startsWith(variables['Build.SourceBranch'], 'refs/tags'))
       strategy:
         matrix:
-          Python35:
-            python.version: '3.5'
+          Python37:
+            python.version: '3.7'
       steps:
         - task: UsePythonVersion@0
           inputs:

qiskit/pulse/commands/command.py

@@ -29,7 +29,7 @@
 
 class MetaCount(ABCMeta):
     """Meta class to count class instances."""
-    def __new__(mcs, name, bases, namespace):
+    def __new__(mcs, name, bases, namespace, **_):
         new_cls = super(MetaCount, mcs).__new__(mcs, name, bases, namespace)
         new_cls.instances_counter = 0
         return new_cls