vty: add 'show rejected-bts'

Print IDs and IPs of recently rejected BTS devices. Example output:

OsmoBSC> show rejected-bts
Date                Site ID BTS ID IP
------------------- ------- ------ ---------------
2018-10-25 09:36:28    1234      0    192.168.1.37

Related: OS#2841
Change-Id: Iba3bfe8fc9432b7ae8f819df8bd71b35b3ec507e
4 files changed