Description of problem:
Detach tier commit operation should not be allowed when detach tier start operation has gone into failed state. There might be files which are not moved from hot to cold tier when a detach tier operation fails. Allowing to commit the operation removes off the hot tier bricks, thereby making those data in hot tier inaccessible.

Version-Release number of selected component (if applicable):
rpm -qa | grep 'gluster'
glusterfs-cli-3.8.3-0.1.git2ea32d9.el7.centos.x86_64
glusterfs-server-3.8.3-0.1.git2ea32d9.el7.centos.x86_64
python-gluster-3.8.3-0.1.git2ea32d9.el7.centos.noarch
glusterfs-client-xlators-3.8.3-0.1.git2ea32d9.el7.centos.x86_64
glusterfs-3.8.3-0.1.git2ea32d9.el7.centos.x86_64
glusterfs-fuse-3.8.3-0.1.git2ea32d9.el7.centos.x86_64
nfs-ganesha-gluster-next.20160813.2f47e8a-1.el7.centos.x86_64
glusterfs-libs-3.8.3-0.1.git2ea32d9.el7.centos.x86_64
glusterfs-api-3.8.3-0.1.git2ea32d9.el7.centos.x86_64
glusterfs-ganesha-3.8.3-0.1.git2ea32d9.el7.centos.x86_64

How reproducible:
Always

Steps to Reproduce:
1. create a tier vol and start detach tier operation
2. kill a brick on hot tier and restore it after a while to fail the detach tier operation
3. Try detach tier commit

Actual results:
detach tier commit is allowed

Expected results:
detach tier commit should not be allowed

Additional info: