Updated endpoints.json for cloudwatch logs to support more regions

Amazon now support us-east-1, us-west-2 and eu-west-1 for cloudwatch logs, but BOTO currently doesn't support these regions 

See https://aws.amazon.com/cloudwatch/faqs/ under "Log Monitoring"
Merge pull request #2685 from djhworld/develop

Updated endpoints.json for cloudwatch logs to support more regions. Fixes #2685.