tcmu-runner: fix bug in EXTENDED_COPY command
tcmu-runner: fix bug in EXTENDED_COPY command

When EXTENDED_COPY command is processed,  data is
readed from rbd image of the source dev,  the data
should be stored in xcopy’s iovec, not in tcmulib_cmd’s
iovec, because the data will be written to rbd
image of the destination dev from xcopy’s iovec,
not from tcmulib_cmd’s iovec

Signed-off-by: Zhaohui Yang <b4b405f30f1470a8859e99e79cace7cb6d77fe9d@umcloud.com>

agrover/tcmu-runner,open-iscsi/tcmu-runner,open-iscsi/tcmu-runner