Remove get_attachment_from_volume()

get_attachment_from_volume() was just used in a single test and that
just extracted a first item from a list of attachments. That seemed
unnecessary to define it as stable interface under tempest.lib.
Then this patch removes get_attachment_from_volume().

Partially implements blueprint consistent-service-method-names

Change-Id: I43c2ec6cc9d3b852602a40d7411ac1e8ea584716
2 files changed