Use newer flake8 to run on ubuntu-focal Zuul machines

flake8 3.6.0  fails on ubuntu-focal zuul machines running python3.8
with the following error:
AttributeError: 'FlakesChecker' object has no attribute 'CONSTANT'

The update removes the version constraint to use newer flake8.  This
also ignores new warnings/errors, which should be addressed in a
future update to remove the ignores

Change-Id: Id22fb14e2cce76c2f4f5234abb3be4db68c70555
Partial-Bug: 1895054
Signed-off-by: Steven Webster <steven.webster@windriver.com>

tox.ini

@@ -44,6 +44,11 @@ commands =
 # E402 module level import not at top of file
 # E501 line too long > 80
 # E722 do not use bare except'
+# E741 ambiguous variable name
+# F series
+# F504 '...' % ... has unused named argument(s):
+# F509 '...' % ... has unsupported format character ','
+# F841 local variable 'e' is assigned to but never used
 # H series are hacking
 # H101: Use TODO(NAME)
 # H102 is apache license
@@ -55,6 +60,7 @@ commands =
 # W291 trailing whitespace
 # W391 blank line at end of file
 # W503 line break before binary operator
+# W504 line break after binary operator
 # B series are from bugbear
 # B001 Do not use bare `except:
 # B007 Loop control variable 'cpu' not used within the loop body.
@@ -62,9 +68,10 @@ commands =
 # B010 Do not call setattr with a constant attribute value
 # F series
 # F401 'module' imported but unused
-ignore = E265,E266,E402,E501,E722
+ignore = E265,E266,E402,E501,E722,E741
+         F504,F509,F841,
          H101,H102,H104,H201,H238,H306,
-         W291,W391,W503,
+         W291,W391,W503,W504
          B001,B007,B009,B010,
          F401
 
@@ -75,7 +82,7 @@ skip_install = True
 deps =
     hacking
     flake8-bugbear<=19.3.0
-    flake8<3.6.0
+    flake8<3.8.3
 commands =
     flake8