Add ProxyUrl parameter for OpenStack builder.

In my particular case I need to use a separate HTTP proxy to access my
OpenStack API than what is set in the environment. This commit adds an
optional parameter to the builder configuration and overrides the
net/http client that is used by the gophercloud library.
Website: Update timeout to reflect real default.

The default in the actual code is 5m.
#450 - allow configuration of manifest dir
website: move iam policy documentation to the root amazon page
website: use user variables in the intro (ec2)
website: user user varibles in the intro (parallel builds)
website: prettyprint variables examle in parallel builds
Return targetPath
https://github.com/mitchellh/packer/issues/578
docs update for https://github.com/mitchellh/packer/issues/578
oops bugfix for work on https://github.com/mitchellh/packer/issues/578
lets try a string instead of a bool for AssociatePublicIpAddress
reverting testing stuff
goamz aspects of AssociatePublicIpAddress working now
working AssociatePublicIpAddress support
revert whitespace changes - not necessary anymore
remove excess debugging
fix some debugging for PublicIpAddress
Update docs
Added option to make ami public automatically