dtrace: Ensure that USDT probes are carried over correctly across fork().

dtrace: Ensure that USDT probes are carried over correctly across fork().

When a process forks, its child will have a copy of the address space of the
parent, and therefore any enabled USDT probes from the parent will also fire
for the child.  In order for those probe firings to be valid, the child must
have its own pid-specific providers (created by duplicating the parent's
providers).

This commit also adds some additional cleanup.

Orabug: 17346878

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>