qemu.tests: fix issue abort can't find_pci device in guest

new device not always should in last line of lspci output, update
pci_find_cmd to reading new device from diff of lscpi output;
Signed-off-by: NXu Tian <xutian@redhat.com>

qemu/tests/pci_hotplug.py

@@ -178,7 +178,7 @@ def run(test, params, env):
                 ref = map(string.strip, reference.splitlines())
                 output = [_ for _ in output if _ not in ref]
                 output = "\n".join(output)
-                if re.search(params.get("match_string"), output, re.I):
+                if re.search(params.get("match_string"), output, re.I | re.M):
                     return True
                 return False
 

tests/cfg/block_hotplug.cfg

@@ -4,7 +4,7 @@
     type = pci_hotplug
     pci_type = block
     reference_cmd = lspci
-    find_pci_cmd = 'lspci | tail -n1'
+    find_pci_cmd = lspci
     images += " stg0"
     boot_drive_stg0 = no
     image_name_stg0 = images/storage0