Clamp pylint to be less than 2.5.0

A new version of pylint was released on April 27 and it is
breaking zuul jobs so submissions cannot merge.

Clamping pylint to be less than 2.5.0 for now.

Change-Id: I77464800aa4ec5b94e10a5e9fbaeb0ddbd2e7845
Partial-Bug: 1875705
Signed-off-by: albailey <Al.Bailey@windriver.com>

test-requirements.txt

@@ -1,4 +1,4 @@
 # hacking pulls in flake8
 hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
 bashate >= 0.2
-pylint
+pylint<2.5.0