virt-host-validate: require fuse for LXC if compiled in

Domains fail to start without fuse like

  error: internal error: guest failed to start: fuse: device not found, try 'modprobe fuse' first
  Failure in libvirt_lxc startup: no error

so check for it too.

References: https://ci.debian.net/data/autopkgtest/unstable/amd64/libv/libvirt/20171012_105903/log.gzReviewed-by: NDaniel P. Berrange <berrange@redhat.com>

tools/virt-host-validate-lxc.c

@@ -93,5 +93,12 @@ int virHostValidateLXC(void)
                                         "BLK_CGROUP") < 0)
         ret = -1;
 
+#if WITH_FUSE
+    if (virHostValidateDeviceExists("LXC", "/sys/fs/fuse/connections",
+                                    VIR_HOST_VALIDATE_FAIL,
+                                    _("Load the 'fuse' module to enable /proc/ overrides")) < 0)
+        ret = -1;
+#endif
+
     return ret;
 }