The pagination for this endpoint has been modified to more closely
model the real AWS behavior:
* Log Groups are now sorted alphabetically by `logGroupName`.
* `nextToken` is now a string containing the last `logGroupName` in the
current response.
* Specifying an invalid `nextToken` does not generate an error, but does
return an empty group list.
* `nextToken` is not included in the response if there are no additional
items to return.
Fixes#3395
9eb58eea41