to address following warning:
fatal: reference is not a tree: 7f02f21f53ccd5e2448086f8e9015489693dd2dc
CMake Error at /home/jenkins-build/build/workspace/ceph-pull-requests/build/fio_ext-prefix/tmp/fio_ext-gitclone.cmake:40 (message):
Failed to checkout tag: '7f02f21f53ccd5e2448086f8e9015489693dd2dc'
it seems that the shallow option does not work with a sha1 tag option,
let's continue using the ceph repo with a tag.
Signed-off-by: Kefu Chai <tchaikov@gmail.com>