add a mapping table from a hash value to a lmaster vnn number

add a mapping table from a hash value to a lmaster vnn number

update ctdb_lmaster() return the lmaster based on this tables contents

initialize the vnn table based on number of nodes for now.
later when recovery is implemented the recovery process will populate
this mapping table.

(This used to be ctdb commit 71e440f6c26ea074f9887237c962101c8cef8c80)