Protect against orte_proc_applied_binding being NULL.

It is now possible for orte_proc_applied_binding to be NULL (e.g., if
you mpirun --bind-to none), so we need to ensure we don't pass it down
to opal_hwloc_base_cset2*str().

Also, take the opprotunity to de-duplicate some strings that are used
in multiple places.

Refs #4073
Fix typo in macro name (#$%@#$% defined-or-not macros!!)

Refs #4079