tests: Add ip6_route_zebra lib function

tests: Add ip6_route_zebra lib function

Add a common function to retrieve and canonicalize
'show ipv6 route' output for use in topotests. Use that in
the test_ospf6_topo1 test; update the corresponding 'expected'
results files to match the lib function.

Replace some 'print' with 'logger' statements in that test also.

Signed-off-by: Mark Stapp <mjs@voltanet.io>