tests: depend on cmk-licensing basics directly in the licensing testlib

license_management.py imports cmk.licensing.basics.*, which the umbrella
//packages/cmk-licensing only provided transitively - basics/ is a separate
package. deballast sees only a dep's direct srcs, so the umbrella looked
unused and was exempted with a keep tag.

Change-Id: I7dd4f421dc725a9560ab9672890b7f65f35e9cc4