Add a step of detaching Compute instance volume if it's created using
the Block Storage service.
It is needed to create a final image.
This commit also moves common volume functions to a different file and
fixes some messages in the StepCreateVolume.
This commit allows user to use the Block Storage v3 volume as the
Compute instance root volume.
Also it adds new volume-related parameters to the builder.
Megan Marsh
Adrien Delorme
Rickard von Essen
Daisuke Takahashi
Andrei Ozerov