Porting baremetal_nodes extension to v2.1/v3

This patch ports baremetal-nodes(include baremetal-stat-ext)
to v2.1 and make v2 and v2.1 share unit test cases.

In v2.1/v3,baremetal-nodes will not depend on baremetal-stat-ext.

Partially implements blueprint v2-on-v3-api
Change-Id: I0f6a968897975ee91e76538d2ce7d2538044613e
Merge "Porting baremetal_nodes extension to v2.1/v3"