Per the ticket, resolve our handling of overload conditions to provide a more consistent response. If we are overloaded (i.e., attempting to bind more processes to a location than the number of cpus under that location), then we consider the following conditions:

(a) default binding policy is in effect. In this case, we will emit a
warning and default to not binding unless the user provided the
"oversubscribe" or "overload" modifier to the "bind-to" option.

(b) user-specified binding policy is in effect. In this case, we will
error out unless the user provided the "oversubscribe" or "overload"
modifier to the "bind-to" option as we cannot meet the directive.

Either "bind-to" modifier (oversubscribe or overload) will be accepted for
now - in 1.9, we will deprecate the "overload" term in favor of
"oversubscribe".

Also added the ability to accept a --bind-to modifier without specifying the binding policy itself so a user can specify overload-allowed with the default policy.

Closes #4345

cmr=v1.8.2:reviewer=rhc:subject=resolve handling of overload conditions