qemu.tests.physical_resource_check: Update memory check pattern

Signed-off-by: NQingtang Zhou <qzhou@redhat.com>

qemu/tests/cfg/physical_resources_check.cfg

@@ -10,7 +10,7 @@
     # Parameter for checking virtio driver's signature in windows guest,
     # useless for linux guest.
     vio_driver_chk_cmd = ""
-    mem_chk_re_str = ([0-9]+)
+    mem_chk_re_str = (\b[0-9]+\b)
     cpu_cores_chk_cmd = "lscpu | grep '^Core'"
     cpu_sockets_chk_cmd = "lscpu | grep -E '(^Socket|^CPU socket)'"
     cpu_threads_chk_cmd = "lscpu | grep '^Thread'"