The NFS daemon service fails to start when `/etc/exports` contains invalid
data. Ivvalid in this contest can mean any of:

1) unknown option
2) unresolved hostname
3) non-existent export path

While failing in case 1) could arguably make some sense, failing in cases 2)
and 3) is rather counter productive - unresolved hostname doesn't necessarily
mean the configuration is bogus - it may well be a hostname  from another 
network. Similarly, 3) can mean it is an export that may appear only under
certain conditions.

Moreover, `exportfs` handles these conditions gracefully and exports only
entries that are valid at the time it is called. Could the behaviour be
reverted to the service starting even with some errors in the exports
definition? As far as I can tell this has been the way for ages.