zebra: Track tables allocated by vrf and cleanup

zebra: Track tables allocated by vrf and cleanup

For each table created by a vrf, keep track of it and
allow for proper cleanup on shutdown of that particular
table.  Cleanup client shutdown to only cleanup data
that the particular vrf owns.  Before we were cleaning
the same table 2 times.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>