Fixes terminate_connection live migration issue

Reverts the changes to cinder/volume/manager.py added in
commit b868ae707f9ecbe254101e21d9d7ffa0b05b17d1 as calling
remove_export in terminate_connection causes Nova live
migration to fail when volumes are attached.

Conflicts:
        cinder/volume/manager.py

Change-Id: I38f3db336db22bb096a8855bcbbfeba16e517b80
Closes-Bug: #1361738
(cherry picked from ddcad011db507cde66b6b1e655d5ffc91ab8880f)
Merge "Fixes terminate_connection live migration issue" into stable/icehouse