qa/suites/fs: add python3-cephfs to packages

qa/suites/fs: add python3-cephfs to packages

the default set of packages to install is in
$suite/qa/packages/packages.yaml . see get_package_list() in
teuthology/teuthology/task/install/__init__.py for how we prepare a
package list for install task.

for running python3 tests in
fs/basic_functional/tasks/volume-client, we need to install
python3-cephfs. please note that,
_package_override() in teuthology/teutholoy/task/install/rpm.py will
take care of the different naming on centos/rhel, where the python3
packages are named python34-*.

Signed-off-by: Kefu Chai <kchai@redhat.com>
(cherry picked from commit 9754b3769bf07af1617ad48376769df016a58d9d)