Several fixes to string handling:
1. strncpy() -> opal_string_copy() (because opal_string_copy()
guarantees to NULL-terminate, and strncpy() does not)
2. Simplify a few places, such as:
* Since opal_string_copy() guarantees to NULL terminate, eliminate
some memsets(), etc.
* Use opal_asprintf() to eliminate multi-step string creation
There's more work that could be done; e.g., this commit doesn't
attempt to clean up any strcpy() usage.
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>