[DOC BLD FIX] Fix indentation in attachments.py
[DOC BLD FIX] Fix indentation in attachments.py

The docstrings for the 'update' function in
cinder/api/v3/attachments.py were not properly indented.
This caused Sphinx warnings to be reported and also caused
the resulting web page to not be properly formatted.

This patch corrects that problem.

Change-Id: Iaca89da8851da8d24f3c0982ff8ae0930e928e39

eharney/cinder,phenoxim/cinder,openstack/cinder,mahak/cinder,Datera/cinder,openstack/cinder,phenoxim/cinder,j-griffith/cinder,j-griffith/cinder,eharney/cinder,Datera/cinder,mahak/cinder