Makefile convenience: add VTY_TEST var to run only one test

VTY transcript tests run all *.vty test scripts, and it is not so
trivial to figure out the test-db creation and cmdline to run only one
of them when debugging. Add VTY_TEST var, useful to pick one test on the
cmdline:

  cd tests
  make vty-test VTY_TEST=test_nodes.vty

Not all VTY tests leave files behind that match hlr_vty_test.db-*, so
make sure that make does not fail it they can't be deleted (rm -f).

Change-Id: I4ad7ddb31b2bfb668b3540cfef658417dd442375
1 file changed