pimd: fix pim interface traffic & pim rp-info json command

pimd: fix pim interface traffic & pim rp-info json command

Issue 1: "show ip pim interface traffic" not show prune TX/RX
Rootcause : not added the variable in the json
Fix : add prune TX/RX in show ip pim interface traffic json

Issue 2: "show ip pim rp-info" not shows the key iAmRp when it is false
Rootcause: Only display the key when the value is true.
Fix: add iAmRp as false in show ip pim rp-info json

Issue 3: "show ip pim rp-info" not showing outbound interface if it is empty
Rootcause: Only display when there is any OIL

Fix: When RP is not reachable then, the outbound interface is Unknown
The command "show ip pim rp-info json" not displaying the outbound
interafce if it is unknown

Signed-off-by: Sarita Patra <saritap@vmware.com>