tests: Allow mgmtd and zebra to fully come up before other daemons

tests: Allow mgmtd and zebra to fully come up before other daemons

Currently the topotest infrastructure is starting up daemons
in mgmtd,zebra, staticd then everything else.

The problem that is happening, under heavy load, is that
zebra may not be fully started and when a daemon attempts
to connect to it, it will not be able to connect.
Some of the daemons do not have great retry mechanisms at all.
In addition our normal systemctl startup scripts actually
wait a small amount of time for zebra to be ready before
moving onto the other daemons.

Let's make topotests startup a tiny bit more nuanced
and have mgmtd fully up before starting up zebra.

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