olpc-update 20->21 fails

[Yioryos Asprobounitis]

In both xo-1 and XO-1.5 olpc-update from os20 to os 21 fails with:

Downloading contents of build 11.2.0_xo1.5-21.
Updating to version hash 27ea7c25580156344ee0286ff6fbc912
Deleting old pristine version b1ffbcd240b61088f8370b6ee0eef2f5
Deleting old run version b1ffbcd240b61088f8370b6ee0eef2f5
/bin/rm: it is dangerous to operate recursively on `/versions/run/b1ffbcd240b61088f8370b6ee0eef2f5' (same as `/')
/bin/rm: use --no-preserve-root to override this failsafe
Deleting old contents for version b1ffbcd240b61088f8370b6ee0eef2f5
Deleting old boot version b1ffbcd240b61088f8370b6ee0eef2f5
Trying irsync_pristine update from rsync://updates.laptop.org/build-11.2.0_xo1.5-21
 - Fetching contents.
Trying irsync_dirty update from rsync://updates.laptop.org/build-11.2.0_xo1.5-21
 - Creating contents for existing tree.
Traceback (most recent call last):
  File "/usr/sbin/olpc-contents-create", line 100, in <module>
    if __name__ == '__main__': main ()
  File "/usr/sbin/olpc-contents-create", line 66, in main
    usermap = mkusermap(options.passwd_file)
  File "/usr/lib/python2.7/site-packages/bitfrost/contents/utils.py", line 58, in mkusermap
    with open(passwd_file) as f:
IOError: [Errno 2] No such file or directory: '/versions/pristine//etc/passwd'
Trying rsync update from rsync://updates.laptop.org/build-11.2.0_xo1.5-21
 - Fetching contents.
No more update methods to try.