rsh: revert part of r32517: keep the quoting

As part of reviewing CMR #4860, I talked through r32517 with Ralph.

In attempt to fix various rsh quoting problems, r32517 removed all the
quoting from the main code path and then only added it back in at the
end in some cases.

This commit puts back the quoting parts that were removed in r32517
(r32517 fixed 2 other important bugs: a) change "--<foo>" to "--mca
<foo_equivalent> 1" so that de-duplication works, and b) change a !=
to ==).

refs #4860