add jolokia_auth option for basic authentication of Jolokia agent

because HTTParty does not support http://username:password@host/jolokia/ form of url.
it can be specified similarly to k24d/fluent-plugin-splunkapi

usage:
  jolokia_auth username:password
Merge pull request #2 from fpt/add-authentication-header

add jolokia_auth option for basic authentication of Jolokia agent