Enable use in top secret AWS regions

[juyoungkim-lisa]

There are at least two items that need to be modified to make use in top secret regions possible.

Endpoint creation based on region (similar to the special case for cn- regions):

• https://github.com/awslabs/collectd-cloudwatch/blob/master/src/cloudwatch/modules/client/requestbuilder.py#L48-L54
• https://github.com/awslabs/collectd-cloudwatch/blob/master/src/cloudwatch/modules/client/ec2requestbuilder.py#L36-L42
• https://github.com/awslabs/collectd-cloudwatch/blob/master/src/cloudwatch/modules/configuration/confighelper.py#L141-L148
• https://github.com/awslabs/collectd-cloudwatch/blob/master/src/cloudwatch/modules/configuration/confighelper.py#L181-L188

There also would need to be modifications to use the top secret region-specific certs. Changes may be needed around:

• https://github.com/awslabs/collectd-cloudwatch/blob/master/src/cloudwatch/modules/client/putclient.py#L31-L54
• https://github.com/awslabs/collectd-cloudwatch/blob/master/src/cloudwatch/modules/client/ec2getclient.py#L27-L39