Clean up tcmu-runner.h
Clean up tcmu-runner.h

Work on a qemu handler highlighted some things we could improve in
tcmu-runner.h. We need to define struct iovec, declare handler_init, and
the name parameter to tcmu_get_attributes can be const.

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>

superlibj/tcmu-runner,open-iscsi/tcmu-runner,JefferyHu/tcmu-runner,mkhon/tcmu-runner,lxbsz/tcmu-runner,yasker/tcmu-runner,open-iscsi/tcmu-runner,liuy/tcmu-runner,rancher/tcmu-runner,agrover/tcmu-runner