Retry additional errors

[jeremywadsack]

The following errors are retriable on Keylime Toolbox API:

• RestClient::ServerBrokeConnection
• Response code 500 is likely retriable
• SocketError

However, the following should not be logged as an error because it's an acceptable response:

Got 404 reading https://app.keylime.io/sites/www-example-com/search_appearances?date=2015-12-16

Let's also clean up error reporting to be more consistent. Right now the script reports errors in two different ways:

ERROR -- : Got RestClient::ServerBrokeConnection reading /sites/www-example-com/gwt_downloads/urls {:date=>"2016-05-04"}
ERROR -- : Got 500 reading https://app.keylime.io/sites/www-example-com/gwt_downloads/urls?date=2017-08-21