Support for all scanner types

Much cleaned up. Supports running behind an ELB as a standalone scanner (helpful for having a real certificate etc) or as a preauth scanner with no ELB. See docs for details.

v0.0.3: do not recreate the nessus instance based on an updated ami. rely on …

…taints instead

v0.0.2: Separated into aws_security_group_rule objects and added support for …

…optional access control via SGs

v0.0.1

first commit