Support adding DHCP interfaces one at a time.

Refactors dhcp-all-interfaces.sh so that if an optional
INTERFACE argument (the first argument) is passed to the script
it only inspects that single interface. If no argument is
passed then the previous default behaviour use used which
causes all interfaces to be inspected.

Also sets PATH so that the commands within the script
can all be found if it isn't set properly (/sbin/ip, /bin/cat, etc.)

This is a move towards using udev rules to add these types
of interfaces automatically.

Change-Id: Ia482c1d3ddce0f0d8d77f9bc3ac76d6924640715

elements/dhcp-all-interfaces/install.d/dhcp-all-interfaces.sh

@@ -1,7 +1,10 @@
 #!/bin/bash
 
+INTERFACE=$1 #optional, if not specified configure all available interfaces
 ENI_FILE="/etc/network/interfaces"
 
+PATH=/bin:/sbin:$PATH
+
 if [ -d "/etc/network" ]; then
     CONF_TYPE="eni"
 elif [ -d "/etc/sysconfig/network-scripts/" ]; then
@@ -63,16 +66,17 @@ function config_exists() {
     fi
 }
 
-for interface in $(ls /sys/class/net | grep -v ^lo$) ; do
-  MAC_ADDR_TYPE="$(cat /sys/class/net/${interface}/addr_assign_type)"
+function inspect_interface() {
+  local interface=$1
+  local mac_addr_type="$(cat /sys/class/net/${interface}/addr_assign_type)"
 
   echo -n "Inspecting interface: $interface..."
   if config_exists $interface; then
     echo "Has config, skipping."
-  elif [ "$MAC_ADDR_TYPE" != "0" ]; then
+  elif [ "$mac_addr_type" != "0" ]; then
     echo "Device has generated MAC, skipping."
-   else
-    ip link set dev $interface up >/dev/null 2>&1
+  else
+    ip link set dev $interface up &>/dev/null
     HAS_LINK="$(get_if_link $interface)"
 
     TRIES=10
@@ -91,4 +95,13 @@ for interface in $(ls /sys/class/net | grep -v ^lo$) ; do
       disable_interface "$interface"
     fi
   fi
-done
+
+}
+
+if [ -n "$INTERFACE" ]; then
+    inspect_interface $INTERFACE
+else
+    for iface in $(ls /sys/class/net | grep -v ^lo$); do
+        inspect_interface $iface
+    done
+fi