PL2445

PL2445

- Reverted to using "du -s" rather than "du -b -s". Note that after
  several cases where the said test failed on a particular PlanetLab
  production machine, I can no longer cause the failure with "du -b -s".
  This indicates that there is something odd going on with vbuild and/or
  the underlying filesystem.

- Fix exit code bug. When the du size test fails, vuseradd will now exit
  with a non-zero code.  This way node manager wont think the
  /vservers/$NAME vserver was created, eventhough it was not.

- Removing slice account from /etc/passwd upon vbuild or "du" error.