test: refactor test-repl-tab-complete

The original test uses a variable to explicitly count how many
times the callback is invoked. This patch uses common.mustCall()
to track if the callback is called or not. This makes the test
more robust, as we don't explicitly hardcode the number of times
to be called.

PR-URL: https://github.com/nodejs/io.js/pull/2122


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>