awslogs streams <group> displays nothing in some situations

If you have a log group that contains streams but those streams were not written to after current_time+5m as calculated by `parse_datetime()`, the streams command will not display them. I would expect `awslogs streams ` to display all the streams inside the group regardless of when they were last written to.

Start at the `awslogs streams ` command and trace how `parse_datetime()` determines which streams are displayed. Done means the command lists every stream in the log group, including streams not written after the calculated current_time+5m.

Written by the indexing model from the issue text.