Ignore non existing files with flake8

This prevents flake8 from showing a "No such file or directory" error
which can occur when running automated checks on deleted files.

Author: zidarsk8

setup.cfg

@@ -1,3 +1,9 @@
 [flake8]
-ignore = E111,E114
+ignore = E111,E114,E902
 max-complexity = 10
+
+# Notes:
+# - E902 is dissabled to prevent IO errors. The automated tests generate a list
+#   of files that were changed (added, removed and edited) and runs the flake8
+#   on those. Disabling this error will prevent false negative tests when a
+#   python file has been removed.