MXS-2067: Replace most SPINLOCKs

Replaced SPINLOCK with std::mutex where possible, leaving out the more
complex cases. The big offenders remaining are the binlogrouter and the
gateway.cc OpenSSL locks.

server/core/utils.cc

@@ -983,8 +983,6 @@ void utils_end()
     replace_values_re = NULL;
 }
 
-SPINLOCK tmplock = SPINLOCK_INIT;
-
 static bool configure_network_socket(int so)
 {
     int sndbufsize = MXS_BACKEND_SO_SNDBUF;