pbrd: make vty nexthop/nexthop-group output consistent

pbrd: make vty nexthop/nexthop-group output consistent

The vty output for pbr maps with a nexthop-group was not
consistent with those configured with an individual nexthop.
Fix that so its easier for users to read.

alfred# show pbr map
  pbr-map TEST1 valid: 1
    Seq: 222 rule: 521
        Installed: yes Reason: Valid
        SRC Match: 2.2.2.2/32
        Nexthop-Group: blue
                Installed: yes Tableid: 10000
    Seq: 333 rule: 632
        Installed: yes Reason: Valid
        SRC Match: 3.3.3.3/32
        Nexthop-Group: blue
                Installed: yes Tableid: 10000
    Seq: 444 rule: 743
        Installed: yes Reason: Valid
        SRC Match: 4.4.4.4/32
        Nexthop-Group: blue
                Installed: yes Tableid: 10000
    Seq: 555 rule: 854
        Installed: yes Reason: Valid
        SRC Match: 5.5.5.5/32
        Nexthop-Group: red
                Installed: yes Tableid: 10001
    Seq: 666 rule: 965
        Installed: yes Reason: Valid
        SRC Match: 6.6.6.6/32
        nexthop 1.1.1.1
                Installed: yes Tableid: 10002
alfred#

Signed-off-by: Stephen Worley <sworley@cumulusnetworks.com>