NETVIRT-1439 : Delete L3VPN cleanup failure.

NETVIRT-1439 : Delete L3VPN cleanup failure.

After running clean script seeing stray fib and vpn configs.

A recent fix to handle cleanup of external PNF flows had broken
footprint cleanup of all other types of FIB entries. This fix made
use of the parentVpnRd attribute in VrfEntry to check for the
footprint of external subnet where the PNFs are discovered (Since,
the footprint/interfaces for that external subnet is maintained in
the VPN of its external network). The parentVpnRf points to this
external network.

The above mentioned fix broke cleanup of existing FIBs since no
other non-PNF fibs will hve their parentVPnRd set.

SO, this fix considers the primaryRd if parentVpnRd is not set.

Change-Id: I3a6f216e9f9cfa6bc6fe1dc8fa7e95b958ebd1b7
Signed-off-by: Kiran N Upadhyaya <kiran.n.upadhyaya@ericsson.com>
Signed-off-by: Achuth Maniyedath <achuth.maniyedath@gmail.com>
Signed-off-by: Achuth <achuth.maniyedath@gmail.com>