cephfs-shell: get command should never create a directory on its own

cephfs-shell: get command should never create a directory on its own

Descrption: When using the get command on a single file, it would append the remote path to
            source path and create directories that shouldn't be created. For instance,
            file 'foo.txt' resides at `/dir1/dir2/` and `get` command is used to copy it to
            /tmp/foo then it would do `/tmp/dir1/dir2/foo.txt` which is not the expected
            behavior. Therefore this PR intends to correct this behavior.

Fixes: https://tracker.ceph.com/issues/55112
Signed-off-by: Dhairya Parmar <dparmar@redhat.com>