cephfs-mirror: use combined output to possibly catch peer import error
cephfs-mirror: use combined output to possibly catch peer import error

By adding a combined output to the executor we might be able to fetch more
error messages.

Signed-off-by: Sébastien Han <62d754cc350e84d3b1c32ae79f976f5348e74a40@redhat.com>

rook/rook,rook/rook,rook/rook,rook/rook,rook/rook