CID 442819 442818 442817: Various Coverity Scan issues in qp-trie tests

Coverity Scan claims the following issues in qp-trie tests on main.

*** CID 442819:  Insecure data handling  (TAINTED_SCALAR)
/tests/libtest/isc.c: 84 in setup_loopmgr()
78     	} else {
79     		/* We always need at least two loops for some of the tests */
80     		workers = isc_os_ncpus() + 1;
81     	}
82     	INSIST(workers != 0);
83     
>>>     CID 442819:  Insecure data handling  (TAINTED_SCALAR)
>>>     Passing tainted expression "workers" to "isc_loopmgr_create", which uses it as an offset.
84     	isc_loopmgr_create(mctx, workers, &loopmgr);
85     	mainloop = isc_loop_main(loopmgr);
86     
87     	return (0);
88     }
89     

*** CID 442818:  Error handling issues  (CHECKED_RETURN)
/tests/bench/load-names.c: 130 in new_rbt()
124      * rbt
125      */
126     
127     static void *
128     new_rbt(isc_mem_t *mem) {
129     	dns_rbt_t *rbt = NULL;
>>>     CID 442818:  Error handling issues  (CHECKED_RETURN)
>>>     Calling "dns_rbt_create" without checking return value (as is done elsewhere 15 out of 16 times).
130     	dns_rbt_create(mem, NULL, NULL, &rbt);
131     	return (rbt);
132     }
133     
134     static isc_result_t
135     add_rbt(void *rbt, size_t count) {

*** CID 442817:  Memory - illegal accesses  (OVERRUN)
/tests/libtest/qp.c: 82 in qp_test_keytoname()
76     	/* Scan the key looking for label boundaries */
77     	for (offset = 0; offset < 512; offset++) {
78     		INSIST(key[offset] >= SHIFT_NOBYTE &&
79     		       key[offset] < SHIFT_OFFSET);
80     		INSIST(loc < 128);
81     		if (key[offset] == SHIFT_NOBYTE) {
>>>     CID 442817:  Memory - illegal accesses  (OVERRUN)
>>>     Overrunning array of 512 bytes at byte offset 512 by dereferencing pointer "key + (offset + 1UL)".
82     			if (key[offset + 1] == SHIFT_NOBYTE) {
83     				locs[loc] = offset + 1;
84     				break;
85     			}
86     			locs[loc++] = offset + 1;
87     		} else if (offset == 0) {