xm-test: Adapt memory setting to up-to-date kernel memory consumption

The attached patch fixes xm-test memset 04 that it can be used with up
to date kernels.  The old version sets the memory to 15MByte which is
too low for modern kernels: the oom-killer in this case kills the
login shell of the test-case and init.  Increased the size to 18M
which gives the userspace about 2.5 MByte memory.

Signed-off-by: Andreas Florath <xen@flonatel.org>

tools/xm-test/tests/memset/04_memset_smallmem_pos.py

@@ -25,7 +25,7 @@ except ConsoleError, e:
     FAIL(str(e))
 
 status, output = traceCommand("xm mem-set %s %i" %
-                              (domain.getName(), 15))
+                              (domain.getName(), 18))
 
 if status != 0:
     FAIL("xm mem-set %s %i returned invalid %i != 0" %