Support S3 FIPS endpoints, disable S3 Transfer Acceleration in GovCloud or FIPS mode

[matt-domsch-sp]

The Fog::AWS::Utils region_to_host method returns the standard S3 endpoints even when ENV['AWS_USE_FIPS_ENDPOINT']=='true'. When FIPS
is called for, and we are in a region where FIPS endpoints are
available, this method should return the FIPS endpoint.

Furthermore, when S3 Transfer Acceleration (S3TA) is requested by
configuration, the above endpoint gets overridden to select the S3TA
endpoint. However, S3TA is not avaialble in GovCloud, and has no FIPS
endpoint equivalents. In this instance, if the region is a GovCloud
region, or if FIPS mode is called for, do not override the endpoint
to use S3TA.

I have a first pass at adding this functionality here for consideration.
#2763

This is functionally equivalent to an issue submitted to the fog-aws project. fog/fog-aws#729

[matt-domsch-sp]

The equivalent patch has been merged into fog-aws upstream. fog/fog-aws#730

[matt-domsch-sp]

#2763 was merged. Closing this ticket.