examples/ubuntu/avahi_client: fix daemon detection

On trusty the `service status` command out doesn't contain "process":
```
$ service avahi-daemon status
avahi-daemon stop/waiting
$ sudo service avahi-daemon start
avahi-daemon start/running
$ service avahi-daemon status
avahi-daemon start/running
```

Change-Id: Id062c8f6ae47eb0a4bf411af6cd0575aef98b815
Reviewed-on: https://weave-review.googlesource.com/1096
Reviewed-by: Vitaly Buka <vitalybuka@google.com>

libweave/examples/ubuntu/avahi_client.cc

diff --git a/libweave/examples/ubuntu/avahi_client.cc b/libweave/examples/ubuntu/avahi_client.cc
index 424cee0..a77e85f 100644
--- a/libweave/examples/ubuntu/avahi_client.cc
+++ b/libweave/examples/ubuntu/avahi_client.cc
@@ -24,7 +24,7 @@
 }  // namespace
 
 MdnsImpl::MdnsImpl() {
-  CHECK_EQ(0, std::system("service avahi-daemon status | grep process || "
+  CHECK_EQ(0, std::system("service avahi-daemon status | grep running || "
                           "service avahi-daemon start"));
   thread_pool_.reset(avahi_threaded_poll_new());
   CHECK(thread_pool_);