Remove the unnecessary option in the  group_vars/all.yml file.

* removed some cinder.conf options like volume_backend_name,
  iscsi_helper, iscsi_protocol etc. these value can be configured by
  custom cinder.conf file, no need export as global variables.
* remove meaningless iscsi_ip_addess, which is not used in LVM driver
* force start iscsi relate when enable_cinder_backend_lvm is yes

TrivialFix
Change-Id: Ifcbfdad15e4d68bc5f20fc77e0315a09983ef022