qubesvm: do not prevent suspend if qubes.SuspendPre fails

The service is called to allow VM to prepare for suspend, but it's just
a notification - if the call fails, suspend anyway.
This especially is important for HVM with PCI devices - if the service
fails, userspace might be not prepared for the suspend, but later
suspend by the kernel in many cases is enough for the VM to recover. If
VM isn't suspended (but paused by Xen instead), it almost never survive
resume.

While at it, improve logging of both service failure and actual suspend
failure.

QubesOS/qubes-issues#6066

qubes/vm/qubesvm.py

@@ -1386,8 +1386,16 @@ async def suspend(self):
             raise qubes.exc.QubesVMNotRunningError(self)
 
         if self.features.check_with_template('qrexec', False):
-            await self.run_service_for_stdio('qubes.SuspendPre',
-                                                  user='root')
+            try:
+                await self.run_service_for_stdio('qubes.SuspendPre',
+                                                 user='root')
+            except subprocess.CalledProcessError as e:
+                self.log.warning(
+                    "qubes.SuspendPre for %s failed with %d (stderr: %s), "
+                    "suspending anyway",
+                    self.name,
+                    e.returncode,
+                    qubes.utils.sanitize_stderr_for_log(e.stderr))
         try:
             self.libvirt_domain.pMSuspendForDuration(
                 libvirt.VIR_NODE_SUSPEND_TARGET_MEM, 0, 0)
@@ -1396,6 +1404,7 @@ async def suspend(self):
                 # OS inside doesn't support full suspend, just pause it
                 self.libvirt_domain.suspend()
             else:
+                self.log.warning("Failed to suspend '%s'", self.name)
                 raise
 
         return self