lib, bgpd: Add ability to specify that some json output should not be pretty

lib, bgpd: Add ability to specify that some json output should not be pretty

Initial commit: 23b2a7ef524c9fe083b217c7f6ebaec0effc8f52
changed the json output of `show bgp <afi> <safi> json` to
not have pretty print because when under a situation where
there are a bunch of routes with a large scale ecmp show
output was taking forever and this commit cut 2 minutes out
of vtysh run time.

Subusequent commit: f4ec52f7cc99f709756d9030623a20c98a086125
changed this back.

When upgrading to latest version the long run time was noticed
due to testing.  Let's add back this functionality such that
FRR can have reduced run times with vtysh when it's really
needed.

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