Replace all random functions with isc_random, isc_random_buf and isc_random_uniform API.

The three functions has been modeled after the arc4random family of
functions, and they will always return random bytes.

The isc_random family of functions internally use these CSPRNG (if available):

1. getrandom() libc call (might be available on Linux and Solaris)
2. SYS_getrandom syscall (might be available on Linux, detected at runtime)
3. arc4random(), arc4random_buf() and arc4random_uniform() (available on BSDs and Mac OS X)
4. crypto library function:
4a. RAND_bytes in case OpenSSL
4b. pkcs_C_GenerateRandom() in case PKCS#11 library

bin/tests/optional/byaddr_test.c

@@ -121,7 +121,7 @@ main(int argc, char *argv[]) {
 	isc_task_setname(task, "byaddr", NULL);
 
 	dispatchmgr = NULL;
-	RUNTIME_CHECK(dns_dispatchmgr_create(mctx, NULL, &dispatchmgr)
+	RUNTIME_CHECK(dns_dispatchmgr_create(mctx, &dispatchmgr)
 		      == ISC_R_SUCCESS);
 
 	timermgr = NULL;