Log the result of command in get_nic_name_by_ip

We need to know the result of the command run
in get_nic_name_by_ip to see what is getting parsed
since we are returning the empty string in some
cases which results in an error because
/var/run/udhcpc..pid does not exist in the guest.

Change-Id: Ie15ac360a7fd384583607d5bf1d8ce7a3d2c3576
Related-Bug: #1813198
diff --git a/tempest/common/utils/linux/remote_client.py b/tempest/common/utils/linux/remote_client.py
index 52ccfa9..49d9742 100644
--- a/tempest/common/utils/linux/remote_client.py
+++ b/tempest/common/utils/linux/remote_client.py
@@ -98,6 +98,7 @@
     def get_nic_name_by_ip(self, address):
         cmd = "ip -o addr | awk '/%s/ {print $2}'" % address
         nic = self.exec_command(cmd)
+        LOG.debug('(get_nic_name_by_ip) Command result: %s', nic)
         return nic.strip().strip(":").split('@')[0].lower()
 
     def get_dns_servers(self):