zebra: Implement recovery for route install failure

zebra: Implement recovery for route install failure

Quagga does not have proper recovery for route install failure (in
the kernel). The lack of this may not be a significant issue if the
failure is only an exception. However, the introduction of route
replace presents a new failure scenario which was not there earlier.
Before replace, the update operation involved a delete followed by
add; the failure of add would not leave hanging route entries in the
kernel as they would've got deleted first. With route replace, if
the replace fails, recovery action to delete the route is needed, else
the route remains hanging in the kernel.

In particular, with VRFs and in the presence of ECMP/multipath, a
failure mode exists where Quagga thinks that routes have been cleaned
up and deleted from the kernel but the kernel continues to retain them.
This happens when multiple VRF interfaces are moved from one VRF to
another.

This patch addresses this scenario by implementing proper recovery for
route install failure.

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Dinesh Dutt <ddutt@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Ticket: CM-10361
Reviewed By: CCR-4566
Testing Done: bgp-min, ospf-min, bgp-smoke, ospf-smoke and manual

Note: There are some test failures and results aren't consistent across
runs; Daniel has resolved many of these through other fixes.