Fixing bug with single instance task and simplifying role setup code

ec2_roles will now accept role names as well as hashes so you can setup
default roles using ec2_roles
allow for setting load balancer as a cap variable rather than having to
pass it for register_instance and deregister_instance
set instance name via the instance task rather than by parsing arguments
so that capify_ec2 will work with multistage builds since position of
server task will not be predictable
always add all roles for a given instance when calling the single
instance task