add back the mysql_base_dir variable to the guest
add back the mysql_base_dir variable to the guest

fixes bug # 1094318
Change-Id: Ie90202695ce6ec6da33a485c45e76f336fa071c0

citrix-openstack/build-trove,changsimon/trove,fabian4/trove,hplustree/trove,citrix-openstack-build/trove,citrix-openstack-build/trove,zhangg/trove,citrix-openstack-build/trove,openstack/trove,fabian4/trove,mmasaki/trove,openstack/trove,hplustree/trove,mmasaki/trove,denismakogon/trove-guestagent,fabian4/trove,cp16net/trove,redhat-openstack/trove,zhujzhuo/openstack-trove,zhujzhuo/openstack-trove,zhujzhuo/openstack-trove,citrix-openstack/build-trove,citrix-openstack/build-trove,zhangg/trove,cp16net/trove,mmasaki/trove,changsimon/trove,redhat-openstack/trove,cp16net/trove,changsimon/trove,denismakogon/trove-guestagent,redhat-openstack/trove