Fixes #3710: Move r28970 to v1.7 branch (Add an option to control)

---svn-pre-commit-ignore-below---

r28970 [[BR]]
Add an option to control which hostnames orte_strip_prefix_from_node_names works
on.

This corrects a problem with Cray systems where the login node's hostname
was being stripped causing the login node to be used as a compute node by
mpirun.

cmr=v1.7.3:reviewer=rhc

r28974 [[BR]]
Refs #3710

Simplify the whole stripping of prefix method by consolidating it into a single MCA param. Allow for multiple prefixes to be stripped, each separated in the param by a comma. If no prefix is given, or the specified prefix isn't in the nodename, then just use the hostname itself.
Remove double free