benchmarks(crazyflie): fix stabilizer.drh

 - add invt
 - add trivial update s.t. (y' = y)...
fix(opensmt/egraph/Enode.C): update print_infix func to add parens for
the arg of pow function

CAPD generates a parsing error when it encouters

    x ^ -3

and asks us to provide

    x ^ (-3)