metrics: Widen libdir and size_hello_obj acceptance window

af881674 shows that the libdir size can
fluctuate quite significantly even when the change is quite small.
Therefore we widen the acceptance window to 10%.

testsuite/tests/perf/size/all.T

-test('size_hello_obj', [collect_size(3, 'size_hello_obj.o')], compile, [''])
+test('size_hello_obj', [collect_size(5, 'size_hello_obj.o')], compile, [''])
 
-test('libdir',[stat_from_file('size', 3, 'SIZE')], makefile_test, ['libdir_size'] )
+test('libdir',[stat_from_file('size', 10, 'SIZE')], makefile_test, ['libdir_size'] )