util: introduce new intmap file parser
schema,mkconst: make route table a string
route: route table api changes

Factor in use of intmap file parser to pull custom route table names
from /etc/iproute2/rt_tables.

To address bnc#885007
route: shift to new route table apis
leasinfo: shift to new route table apis
client: shift to new route table apis
iflist: shift to new route table apis
dbus: shift to new route table apis and process route table as string per schema