Add support for LDAP authentication in Livy Server

Currently, Livy doesn't support LDAP Authentication from client(sparkmagic) to server(livy). We need to add LDAP authentication as that's preferable method due to security reasons. We won't be able to use Knox for this purpose. That is why I am raising this PR which contains LDAP authentication. I have upgraded hadoop.version in livy-main to 2.8.0 as this version contains LivyAuthenticationHandler. Below I have mentioned link for the same:
https://insight.io/github.com/apache/hadoop/blob/HEAD/hadoop-common-project/hadoop-auth/src/main/java/org/apache/hadoop/security/authentication/server/LdapAuthenticationHandler.java