MORE Allow for EXPORT config of export_id = 0

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>
Fix return code in nfs_export_get_root_entry

If cache_inode_new_entry returned CACHE_INODE_ENTRY_EXISTS,
nfs_export_get_root_entry would pass that on to it's caller,
which is not right, all it cares is that the entry was found
and usable.

Signed-off-by: Frank S. Filz <ffilzlnx@mindspring.com>