opal_string_copy() takes care of all the string computations.
Specifically: when we converted to opal_string_copy(), we accidentally
left the *source* length as the argument, not the *target* length,
which resulted in one less character being copied than intended (as
was showing up in MTT C++ testing results).
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>