Small fixes after stress test

[austinbyers]

to: @chunyong-lin cc: @airbnb/binaryalert-maintainers size: small

Background

112 , #113 , and #114 were some relatively big changes to BinaryAlert, and some problems surfaced when stress-testing in different environments, which we address here.

Changes

• Use subprocess instead of pip.main, which is no longer supported in pip v10.0.0
• Change Downloader metadata to accommodate a wider range of possibilities introduced by the new cbapi
• Remove units from CloudWatch graph titles (CloudWatch now shows them in the graph itself)
• Fix the DLQ metric alarm - it should look at number of messages, not messages received
• SQS retention has been lowered from the default (4 days) to 12 hours, mostly so that the graph of message age is easier to see. In practice, messages should never stick around that long

Testing

• Deployed to other environments

[coveralls]

Coverage remained the same at 93.009% when pulling 08043c010fcc73c0b7c08ce6a9eaf2c01b92d5dc on austin-small-fixes into 60cc102beecb7463b363fc414620508e6b268e9b on master.