Ironic and baremetal install diskimage-builder with pip

This change installs diskimage-builder with pip instead
of from git, and only if the executable ramdisk-image-create
isn't already installed.

This allows the ironic and baremetal to consume the latest
release of diskimage-builder by default, and gives the option of
defining version constraints for which version to install.

If the dib service is enabled (which it isn't by default) then
diskimage-builder will already be installed from git and will
not be re-installed for ironic and diskimage-builder.

Change-Id: Ic6613a11e2c4fb7a1261b81cdc2cf958515e60cd
Install heat-cfntools and heat-templates repos

These projects contain agents which can be installed on custom
images. Installing these repos will allow a future change to
build a custom image containing these projects. This will allow
gating on any changes in these projects by running heat-slow
on the custom image.
The corresponding devstack-gate change is
https://review.openstack.org/#/c/92055/
Change-Id: I7b1343c094f755f79ddeb1bac3ff4c0daa3fb70c
A service to install diskimage-builder

Enabling service 'dib' will install the following repos:
* diskimage-builder
* tripleo-image-elements
* os-collect-config
* os-refresh-config
* os-apply-config

These repos are already pre-fetched in devstack-gate.

This will facilitate gating on changes in these projects by building
a custom image then running the heat-slow job against that image.

diskimage_builder is pip installed from the current git checkout
if the dib service is enabled. This allows devstack gating on
diskimage-builder changes while also allowing diskimage-builder to
be installed from releases for other scenarios (for example, ironic).

Change-Id: Ia911cdee86f5b2e2ba1557e5aa8bf392b92ef555
Latest tox should work for openstack now, use it

Remove the tox pin that was in place to avoid issues with tox 1.7.0 and
1.7.1. Latest tox (1.7.2) is compatbile with openstack's tox.ini files
again and should work with tempest. This change is self testing and will
confirm this.

Making this change is important so that devs can stop worrying about
package version pins and helps ensure we don't get left behind by
upstream.

Change-Id: Ibf2102d6ad439dd354ae687f7aafec9ceca6cf9c
Merge "Ironic and baremetal install diskimage-builder with pip"
Merge "Install heat-cfntools and heat-templates repos"
Merge "A service to install diskimage-builder"
Merge branch 'master' of https://github.com/openstack-dev/devstack