* Use context in aws DescribeRegionsWithContext
In the current way, DescribeRegions is used which doesn't allow
cancelling the request if the context changes. Using
DescribeRegionsWithContext is the preferred way.
* Fix context variable
* Revert GetRegionsWithContext to GetRegions
GetRegions is not an AWS SDK method. Hence, GetRegions should be enough
as the name change is not needed for context implementation.