Introduce support for AmarisoftEPC

* A new abstract generic base class EPC is created
* srsEPC and AmarisoftEPC inherit from that class
* options are loaded from defaults.conf in cascade. First generic "epc",
  afterwards the specific enb type.
* A new scenario is added to select the EPC type to use. srsEPC is the
  default unless stated by an scenario.
* AmarisoftEPC delegates setup of the tun IP address to an "ifup"
  script. As a result, since we run without root permissions (ony with
  CAP_NET_ADMIN), the ifup script itself is unablet o set the IP
  address. To solve this, we introduce a new osmo-gsm-tester helper
  script which must be installed in the slave node which can be called
  through sudo to increase privileges to do so.

With this commit, I can already get srsUE<->amarisoftENB<->amarisoftEPC
to pass ping and iperf3 4g tests.

Change-Id: Ia50ea6a74b63b2d688c8d683aea11416ad40a6d3
diff --git a/utils/bin/osmo-gsm-tester_amarisoft_ltemme_ifup.sh b/utils/bin/osmo-gsm-tester_amarisoft_ltemme_ifup.sh
new file mode 100755
index 0000000..d502123
--- /dev/null
+++ b/utils/bin/osmo-gsm-tester_amarisoft_ltemme_ifup.sh
@@ -0,0 +1,16 @@
+#!/bin/bash -e
+ifname="$1"     # Interface name
+index="$2"      # Network index (PDN index)
+apn="$3"        # Access point name
+type="$4"       # ipv4 or ipv6
+ifaddr="$5" # Interface address
+addr1="$6"  # First IP address
+addr2="$7"  # Last IP address
+mask="$8"   # Mask
+echo "*** Configuring $type APN[$index] '$apn' on ${ifname}, $ifaddr/$mask, ${addr1}..${addr2}"
+if [ "$type" = "ipv4" ] ; then
+        ifconfig ${ifname} ${ifaddr}/${mask} up
+else
+        ifconfig ${ifname} inet6 add ${addr1}/${mask} up
+fi
+echo "*** done configuring interface ${ifname}"