Re-add accidentally removed update_version.sh

Last commit removed this file accidentally.

Change-Id: I030f927af26d4750e88662e591cde3eea6b810c7

update_version.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+set -e
+git describe --abbrev=8 --dirty | sed 's/v\([^-]*\)-\([^-]*\)-\(.*\)/\1.dev\2.\3/' > version
+cat version
+echo "# osmo-gsm-tester version.
+# Automatically generated by update_version.sh.
+# Gets imported by __init__.py.
+
+_version = '$(cat version)'" \
+  > src/osmo_gsm_tester/_version.py