Add logging and retry label change

Sometimes the label change HTTP request can fail; in those cases,
try 3 times 5 seconds apart, and then log the error.

Change-Id: Ifab68c91b89edfc5b441cbcabd1035efdc3a148e
Add a check script

It can be used to periodically test that each node is reachable
over ssh.  If not, the node is deleted.

Fixes bug: 1130414

Change-Id: If3945342e83dc7d05c6384244dd6306071c8eca0
Merge "Add logging and retry label change"
Merge "Add a check script"