This updates the description of the
'PUT /v1/nodes/{node_ident}/states/power' request to mention that
Bare Metal API version 1.27 was when:
- the 'timeout' parameter was added
- the 'soft power off' and 'soft rebooting' values were made available
for the 'target' parameter
Change-Id: I1c720a2dd15eab1246ad672b9d7f2b8708ceec0b