Make 'mappings' CLI output user friendly

Make 'mappings' CLI output user friendly

Before this patch, the mappings CLI command would print out the full
Java objects contained in a map-cache. That's great for in-depth
debugging, but for a quick look it very hard to read. This patch
implements a user friendly CLI output for mappings, to improve
readability.

The old full output is still available in Karaf, but is by adding the
'-d' or '--debug' switch to the CLI command.

Example output:

---8<--------------------------------------------------------------------
opendaylight-user@root>mappings
Policy map-cache
----------------
Instance ID 1
  [1] 192.0.2.1/32|192.0.2.2/32, TTL: 1440
    -> Locator                                         State     Pri/Wgt
       10.10.10.10                                     no-route  1/1

Southbound map-cache
--------------------
Instance ID 0
  192.0.2.1/32, TTL: 1440
    -> Locator                                         State     Pri/Wgt
       192.168.16.21                                   up        1/1
       fdab:cc19:b80e::21                              up        1/1
       -----------------------------------------------------------------
    -> Subscriber RLOC                                 Subscriber EID
       192.168.16.21                                   No Address Present
       127.0.0.2                                       No Address Present
-------------------------------------------------------------------->8---

Change-Id: Id3c304ac9eda77a0cc36bff1cdeb18d61608a796
Signed-off-by: Lorand Jakab <lojakab@cisco.com>