Fix devflow build system

Make devflow-update-version directly update version.m4

VERSION

-2.1.1
\ No newline at end of file

devflow.conf

 [ packages ]
   [[ blktap-archipelago ]]
-    version_file = ""
-  [[ blktap-archipelago-dev ]]
-    version_file = ""
-  [[ blktap-archipelago-utils ]]
-    version_file = ""
-  [[ libvhd0-archipelago ]]
-    version_file = ""
-  [[ libvhd0-archipelago-2.1rc1 ]]
-    version_file = ""
-  [[ libblktapctl0-archipelago ]]
-    version_file = ""
+    version_file = "version.m4"
+    version_template = "version_template"

version.m4

-m4_define([BLKTAP_VERSION], [m4_include(VERSION)])
+m4_define([BLKTAP_VERSION], [2.1])

version_template

+m4_define([BLKTAP_VERSION], [%(DEVFLOW_VERSION)s])