Move global glance opts into nova.image.glance

Move the glance_host, glance_port and glance_protocol options into the
nova.image.glance module.

Also move the generate_glance_url() and generate_image_url() utility
methods there since they're the only uses of the options outside of the
module.

blueprint: scope-config-opts
Change-Id: I3beca1a65cdd902a94ddc1c512d79a4de635ef38
Merge "Move global glance opts into nova.image.glance"