Fix: Bad return error code handling

Two things here. First, if the tracer dies before we have time to create
the session on it, the returned value (-1) was not handled creating a
segfault on the following loop.

Second, we no longer assert on the application PID hash table delete
return value since we use add_replace on app. registration creating a
possible key reuse for a different node.

Signed-off-by: David Goulet <dgoulet@efficios.com>