tests: Ensure connected routes are installed before continuing

tests: Ensure connected routes are installed before continuing

Upon high load the ospf_instance_redistribute test can attempt
to install routes with sharpd before the connected routes have
fully baked themselves into zebra.  Since sharpd intentionally
has no retry mechanism we need to ensure that the test is waiting
a small bit.

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