Use Literal Blocks to write code sample in docstring

In python docstring, one should use Literal Blocks to write sample
code otherwise one gets build warnings and badly formatted documents.

Also, because sphinx treats the line which starts ".." as a comment,
this patch moves "..." to the end of the previous line.

Change-Id: I0bbd61d43daaffe9de579b1a6b50ea6826bdfd50
Partial-bug: 1277282
Do not strip 'glance://' prefix from image hrefs

pxe_utils.get_deploy_kr_info and drivers.modules.pxe._get_image_info
functions strip 'glance://' prefix from image references while it's
not necessary as Glance service can download images by such refs.
Also some refactoring done as these references are not just uuids.

Partially implements: blueprint non-glance-image-refs

Change-Id: Ie0d87c96c80dab23ea81011413600d9dbbf50177
Merge "Use Literal Blocks to write code sample in docstring"
Merge "Do not strip 'glance://' prefix from image hrefs"