website: user Variables in Intro

builder/amazon/ebs: AssociatePublicIpAddress for launching

This reverts commit b2fc77870b825403ea068ba63f66ac28c76b3e88, reversing
changes made to 4789d3acc8937757ee7a430199bbc39671ba93c7.

This is already possible by setting groups.

builder/amazon/all: added option to make AMI public 

builder/openstack: add ProxyUrl parameter for OpenStack builder

builder/qemu: qemu format img is invalid

builder/vmware: trivial bug fix in mechanism to clean installation ISOs for VMware build...

The resolution of Bug #608 still had issues.  This change removes a
superfluous period.

Testing Done:
- built packer with my change
- built VMware VMs and saw that the vmx file had the expected
  changes.