tests: Add some tests to show new behavior works as expected

tests: Add some tests to show new behavior works as expected

a) A noprefix address by itself should not create a connected route.
   This was pre-existing.
b) A noprefix address with a corresponding route should result in a
   connected route.  This is how NetworkManager appears to work.
   This is new behavior, so a new test.
c) A route is added to the system from someone else.
   This is new behavior, so a new test.

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