Update slice.py to use CM v2 API, and add a command to rsync to all nodes.
Update slice.py to use CM v2 API, and add a command to rsync to all nodes.

This rsync feature should work as an interim measure to give users
an easy way to keep filesystem state (especially configuration files,
rc files, etc.) consistent on all nodes across a slice.  In the long
term, some sort of shared and/or persistent filesystem capability would
be nicer.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome