cephfs: upgrade cephfs-shell's path wherever necessary

cephfs: upgrade cephfs-shell's path wherever necessary

Commit dc69033763cc116c6ccdf1f97149a74248691042 moves cephfs-shell from
"<CEPH-REPO-ROOT>/src/tools/cephfs/" to
"<CEPH-REPO-ROOT>/src/tools/cephfs/shell" but cephfs-shell's location in
src/vstart.sh and qa/tasks/cephfs/test_cephfs_shell.py is left
un-updated. This produces a broken vstart_environment.sh and broken
export command in test_cephfs_shell.py.

Introduced-by: dc69033763cc116c6ccdf1f97149a74248691042
Fixes: https://tracker.ceph.com/issues/58795
Signed-off-by: Rishabh Dave <ridave@redhat.com>
(cherry picked from commit 48ef0444774934dd6d0d3e026142d95e4098bebd)

 Conflicts:
	qa/tasks/cephfs/test_cephfs_shell.py
	- Comment present at the top of file was different in Pacific
	  compared to main branch.