Add timestamp to last scans

Ex:
  no.nordicsemi.android.mcp (Registered)
  LE scans (started/stopped)       : 5 / 4
  Scan time in ms (min/max/avg)    : 97 / 1476 / 897
  Last 4 scans (timestamp - duration):
    1970/02/13 21:10:19 - 1476ms
    1970/02/13 21:10:21 - 97ms
    1970/02/13 21:10:23 - 929ms
    1970/02/13 21:10:25 - 531ms
  Application ID                   : 5
  UUID                             : f77437a1-5e86-4e2d-8223-6193a095c7f5
  Current scan duration in ms      : 1452
  Connections: 0


Bug: 27294154
Change-Id: I66ba6b4bc2d45ced7d6414db007394a16a30956e