Support OpenSwan in Neturon VPNaaS

Neutron VPNaaS chagned ipsec package for
OpenSwan. This commit updates the package.

Change-Id: I333501a405fbc552c575d26cfbac083646d05dfd
diff --git a/lib/neutron_plugins/services/vpn b/lib/neutron_plugins/services/vpn
index 0a79a69..b8f5c7d 100644
--- a/lib/neutron_plugins/services/vpn
+++ b/lib/neutron_plugins/services/vpn
@@ -8,9 +8,10 @@
 
 AGENT_VPN_BINARY="$NEUTRON_BIN_DIR/neutron-vpn-agent"
 VPN_PLUGIN="neutron.services.vpn.plugin.VPNDriverPlugin"
+IPSEC_PACKAGE=${IPSEC_PACKAGE:-"openswan"}
 
 function neutron_vpn_install_agent_packages() {
-    install_package strongswan
+    install_package $IPSEC_PACKAGE
 }
 
 function neutron_vpn_configure_common() {