packer: required user variables [GH-374]
packer: fix required var check to work properly
website: document required user vars
command/inspect: show required variables differently
command/inspect: cleaner output if no required vars
builder/digitalocean: retry destroy a few times
If PKCS1 parsing of the SSH key fails, try PKCS8
If no image is generated, just return nil for the Openstack provider

This mirrors what is done in other providers e.g. Amazon providers
Merge pull request #375 from justinsb/avoid_nil_pointer_if_no_openstack_image

builder/openstack: If no image is generated, just return nil
Update CHANGELOG
Merge pull request #376 from justinsb/try_parse_pkcs8

communicator/ssh: If PKCS1 parsing of the SSH key fails, try PKCS8
Update CHANGELOG
Support IPv6 access address for Openstack

We still prefer the IPv4 address, but if there is an IPv6 address and no IPv4 address, use IPv6.
website: page titles on provisioner docs
website: fix typo s/script/shell/ provisioner
builder/openstack: don't hardcode "DFW" and make region required
website: document required openstack region setting
website: fixup some underscores to not be emphasis in the AWS docs
website: add openstack to the intro platforms list
builder/openstack: region is now required