Upgrade pylint to a new version that works with python3.7

The pylint and astroid version should be specified for python3.7
pylint==2.3.1
astriod==2.1.0

Change-Id: I5aa7676b18beafc50d3f773f488e5dbe30e62035

.pylintrc

@@ -44,7 +44,7 @@ symbols=no
 # --enable=similarities". If you want to run only the classes checker, but have
 # no Warning level messages displayed, use"--disable=all --enable=classes
 # --disable=W"
-disable=W,C,R,E1002,no-member
+disable=W,C,R,E1002,no-member,assignment-from-none
 
 
 [REPORTS]

test-requirements.txt

@@ -2,7 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 flake8<2.6.0,>=2.5.4 # MIT
-pylint==1.9.2 # GPLv2
+#pylint==1.9.2 # GPLv2
 hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 mock>=2.0.0 # BSD
@@ -15,3 +15,7 @@ testtools>=2.2.0 # MIT
 os-api-ref>=1.4.0 # Apache-2.0
 reno>=2.5.0 # Apache-2.0
 openstackdocstheme>=1.18.1 # Apache-2.0
+astroid==1.6.5;python_version<"3.0" # LGPLv2.1
+astroid==2.1.0;python_version>="3.0" # LGPLv2.1
+pylint==1.9.2;python_version<"3.0" # GPLv2
+pylint==2.3.1;python_version>="3.0" # GPLv2