Address linter errors and warnings

[sajith]

Here's a summary (from this CI run, but it isn't really specific to that CI run in particular):

4     E111 indentation is not a multiple of 4
1     E265 block comment should start with '# '
94    E501 line too long (80 > 79 characters)
2     E711 comparison to None should be 'if cond is None:'
1     E712 comparison to True should be 'if cond is not True:' or 'if not cond:'
29    F401 'os' imported but unused
5     F403 'from swagger_server.messaging.topic_queue_consumer import *' used; unable to detect undefined names
10    F405 'TopicQueueConsumer' may be undefined, or defined from star imports: swagger_server.messaging.topic_queue_consumer, swagger_server.utils.db_utils
1     F811 redefinition of unused 'dataset' from line 1
14    F841 local variable 'e' is assigned to but never used
1     W291 trailing whitespace

Some of these could be cleaned up. The one one about overlong lines could be either ignored, or black and flake8 could be made to agree with each other.