[trac606] added ability to change the location of config file runtime.

this is one of prerequisites to perform various system tests.

src/bin/cfgmgr/b10-cfgmgr.py.in

@@ -26,10 +26,18 @@ import os
 isc.util.process.rename()
 
 # If B10_FROM_SOURCE is set in the environment, we use data files
-# from a directory relative to that, otherwise we use the ones
-# installed on the system
+# from a directory relative to the value of that variable, or, if defined,
+# relative to the value of B10_FROM_SOURCE_CONFIG_DATA_PATH.  Otherwise
+# we use the ones installed on the system.
+# B10_FROM_SOURCE_CONFIG_DATA_PATH is specifically intended to be used for
+# tests where we want to use variuos types of configuration within the test
+# environment.  (We may want to make it even more generic so that the path is
+# passed from the boss process)
 if "B10_FROM_SOURCE" in os.environ:
-    DATA_PATH = os.environ["B10_FROM_SOURCE"]
+    if "B10_FROM_SOURCE_CONFIG_DATA_PATH" in os.environ:
+        DATA_PATH = os.environ["B10_FROM_SOURCE_CONFIG_DATA_PATH"]
+    else:
+        DATA_PATH = os.environ["B10_FROM_SOURCE"]
 else:
     PREFIX = "@prefix@"
     DATA_PATH = "@localstatedir@/@PACKAGE@".replace("${prefix}", PREFIX)