Consumer context beanName prefix

- Avoid using hardcoded prefix for bean definitions within consumer context
which breaks the placeholder syntax
 - If there are more than one consumer configurations then, the bean names
will have hard-coded prefix along with groupId. otherwise, simple hardcoded
beanNames are sufficient. This will allow us to use placeholder values which
could be resolved in later phase. 

This change is specifically needed for using kafka inbound channel adapter as Spring XD source module where there could be a single consumer configuration and the placeholder values for that consumer config are resolved from module options.