tests: fix typo in test_vlib

tests: fix typo in test_vlib

Trailing comma made last line of a multi-line command a new command.

Logs:
  22:39:49,695 Return value: cli_inband_reply(_0=794, context=2, retval=0, reply='loop0\n')
  22:39:49,695 CLI: packet-generator new {
   name vlib
   limit 15
   size 128-128
   interface loop0
   node ethernet-input
   data {
     IP6: 00:d0:2d:5e:86:85 -> 00:0d:ea:d0:00:00
     ICMP: db00::1 -> db00::2
     incrementing 30
     }

  22:39:49,695 Calling cli_inband('cmd':'packet-generator new {\n name vlib\n limit 15\n size 128-128\n interface loop0\n node ethernet-input\n data {\n   IP6: 00:d0:2d:5e:86:85 -> 00:0d:ea:d0:00:00\n   ICMP: db00::1 -> db00::2\n   incrementing 30\n   }\n\n','context':3,'_vl_msg_id':792)
  22:39:49,696 Return value: cli_inband_reply(_0=794, context=3, retval=0, reply='')
  22:39:49,696 CLI: }

  22:39:49,696 Calling cli_inband('cmd':'}\n\n','context':4,'_vl_msg_id':792)
  22:39:49,697 Return value: cli_inband_reply(_0=794, context=4, retval=-1, reply="unknown inpu...
  22:39:49,697 }
   FAIL reply unknown input `}'

Type: fix

Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
Change-Id: Iaa82d432677d742e766e42383364adda5bd87665