xenopsd: the keys in the config file are 'vbd-' not 'block-'

Signed-off-by: David Scott <dave.scott@citrix.com>
xenopsd: work around lack of vncterm user and groups

On Ubuntu, the post-install actions don't seem to work and the necessary
groups don't exist. We check for them on every invocation in a wrapper
script.

Signed-off-by: David Scott <dave.scott@citrix.com>