Allow nonzero puppet exit codes when launching

* launch/launch-node.py: Now that we're using --detailed-exit-codes
with puppet, we should not abort when the ssh call exits nonzero.
Puppet explicitly returns nonzero codes which indicate success
conditions, and we already have a function in place to interpret
them.

Change-Id: If66d345902d05fa0898d202f5f71c087df9f4ce7
Merge "Allow nonzero puppet exit codes when launching"