Allow to run the test-suite in parallel when more versions are built

Related: #1969430

mysql.spec

@@ -611,8 +611,11 @@ pushd %_vpath_builddir
 make test VERBOSE=1
 pushd mysql-test
 cp ../../mysql-test/%{skiplist} .
-# builds might happen at the same host, avoid collision
-export MTR_BUILD_THREAD=%{__isa_bits}
+
+# Builds might happen at the same host, avoid collision
+#   The port used is calculated as 10 * MTR_BUILD_THREAD + 10000
+#   The resulting port must be between 5000 and 32767
+export MTR_BUILD_THREAD=$(( $(date +%s) % 2200 ))
 
 ./mtr %{?with_debug:--debug-server} \
   --parallel=auto --force --retry=2 \