random-util: rename acquire_random_bytes() → genuine_random_bytes()

It's more descriptive, since we also have a function random_bytes()
which sounds very similar.

Also rename pseudorandom_bytes() to pseudo_random_bytes(). This way the
two functions are nicely systematic, one returning genuine random bytes
and the other pseudo random ones.

src/firstboot/firstboot.c

@@ -647,7 +647,7 @@ static int process_root_password(void) {
         if (!arg_root_password)
                 return 0;
 
-        r = acquire_random_bytes(raw, 16, true);
+        r = genuine_random_bytes(raw, 16, true);
         if (r < 0)
                 return log_error_errno(r, "Failed to get salt: %m");