BUG-2627: Fix ambiguous lookup in test case

Looking up by java name "stream" matches two potential beans, which
means that the returned value depends on underlying collections. This
breaks when upgrading to Java 8, for example.

Fix by performing an explicit prefix name, which returns the right bean
everytime.

Change-Id: I4c7f7f26bc00cc1b03b9ea99ef84004da46c3caa
Signed-off-by: Robert Varga <rovarga@cisco.com>