Support detection of interfaces with non-word chars in the name

The current regex only matches host interface names that consits
of "word characters" (regex \w). Intefaces having other special
chars like "-" or "." are not parsed. Examples that are not yet
matched are br-ex (ovs bridge) or enccw0.0.1234 (s390 eth device
name).

In addition it's hard to understand the the regex.

This fix is replacing the regex by a simple awk statement also
matching those names.

In addition the determination of the host_ip_iface was moved
down into the if clause, as it is only used inside.

Change-Id: I3d1b1afa32956e4e8c55c7e68cbafaf8e03e7da2
Closes-Bug: #1429903
diff --git a/functions-common b/functions-common
index 4739e42..ed43e20 100644
--- a/functions-common
+++ b/functions-common
@@ -542,11 +542,11 @@
     local host_ip_iface=$3
     local host_ip=$4
 
-    # Find the interface used for the default route
-    host_ip_iface=${host_ip_iface:-$(ip route | sed -n '/^default/{ s/.*dev \(\w\+\)\s\+.*/\1/; p; }' | head -1)}
     # Search for an IP unless an explicit is set by ``HOST_IP`` environment variable
     if [ -z "$host_ip" -o "$host_ip" == "dhcp" ]; then
         host_ip=""
+        # Find the interface used for the default route
+        host_ip_iface=${host_ip_iface:-$(ip route | awk '/default/ {print $5}' | head -1)}
         local host_ips=$(LC_ALL=C ip -f inet addr show ${host_ip_iface} | awk '/inet/ {split($2,parts,"/");  print parts[1]}')
         local ip
         for ip in $host_ips; do