Fix bugs introduced from #642

[austinbyers]

to: @ryandeivert or @chunyong-lin
cc: @airbnb/streamalert-maintainers
size: small

Background

When syncing #642 internally, we found a couple of bugs related to rule testing. Namely:

• The output credentials bucket was not mocked correctly because it had the wrong name
• The mocks for the threat intel table and the alerts table conflict with each other

Changes

• Reverted name of the secrets bucket in the alert processor (prefix.streamalert.secrets is correct, not prefix_streamalert_secrets)
• Remove @mock_dynamodb2 decorator from methods which setup mock tables, because the context is already mocked when those methods are called

Testing

• Deployed this to a test account and tested the slack integration (to confirm output secrets are working as expected). Going forward, I'll make sure to test outputs with secrets when making large changes to the alert processor.
• Synced this branch internally and all tests pass

[ryandeivert]

🐑

[coveralls]

Coverage remained the same at 95.554% when pulling 0a9ed21 on austin-rule-tests into 7d2804d on master.