[SPARK-4075] [Deploy] Jar url validation is not enough for Jar file

In deploy.ClientArguments.isValidJarUrl, the url is checked as follows.

    def isValidJarUrl(s: String): Boolean = s.matches("(.+):(.+)jar")

So, it allows like 'hdfs:file.jar' (no authority).

space before should, but I'll fix this when I merge