Add an implicit node name label for scheduling pods.

This enables easy scheduling to specific nodes, which is a requirement for a "pod per node" controller.

See #1518 
for 1) Yes, I realized this is the goal.  My concern is that apart from label "ssd=true", this change also added "$.name=nodename" to match, which could fail to match because pod selector generally won't give a node name selector.

for 2) I thank label is matched by 'and term', so even if name label presents, changes to other label will fail the match.