Make dialogs more reusable

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
Merge branch 'patch-reusable-dialogs' of github.com:battlemidget/openstack-installer into patch-reusable-dialogs

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>

Conflicts:
	cloudinstall/install.py
	cloudinstall/ui/__init__.py
	cloudinstall/ui/dialog.py
	cloudinstall/ui/input.py