Adjust behaviors of cbq's '-a' flag and non batch mode.

MB-35490 shows a few usability issues:

1. The -a or -analytics flag enables two features: auto discovery of an Analytics node in the cluster (instead of a Query node, which is the default) and batch mode.
2. It is necessary to use batch mode for requests that use SET or USE statements for requests to the Analytics Service.

To alleviate these issues we could

1. only enable connections to an Analytics node using the -a flag (and not enable batch mode at the same time) and
2. require the -b flag to enable batch mode and
3. collect SET and USE statements (which are basically request-scoped declarations that do not have an effect if they are not followed by an executable statement) to submit them together with a following executable statement.