Move the isc_random API initialization to the thread_local variable

Instead of writing complicated wrappers for every thread, move the
initialization back to isc_random unit and check whether the random seed
was initialized with a thread_local variable.

Ensure that isc_entropy_get() returns a non-zero seed.

This avoids problems with thread sanitizer tests getting stuck in an
infinite loop.

lib/isc/lib.c

@@ -26,7 +26,6 @@
 #include "mem_p.h"
 #include "mutex_p.h"
 #include "os_p.h"
-#include "random_p.h"
 
 #ifndef ISC_CONSTRUCTOR
 #error Either __attribute__((constructor|destructor))__ or DllMain support needed to compile BIND 9.
@@ -46,7 +45,6 @@ isc__initialize(void) {
 	isc__os_initialize();
 	isc__mutex_initialize();
 	isc__mem_initialize();
-	isc__random_initialize();
 	isc__tls_initialize();
 	isc__uv_initialize();
 	isc__xml_initialize();