Introduce get_python_exec_prefix function.

get_python_exec_prefix returns the path to the direcotry where python
executables are installed, that is /usr/bin on Fedora and /usr/local/bin
everywhere else.

It is used to properly locate OpenStack executables.

Fixes: bug #1068386

Change-Id: I228498ebe2762568d00757d065e37377ee2c8fb3
diff --git a/lib/ceilometer b/lib/ceilometer
index 0fae397..41a5f53 100644
--- a/lib/ceilometer
+++ b/lib/ceilometer
@@ -40,7 +40,7 @@
 if [ -d $CEILOMETER_DIR/bin ] ; then
     CEILOMETER_BIN_DIR=$CEILOMETER_DIR/bin
 else
-    CEILOMETER_BIN_DIR=/usr/local/bin
+    CEILOMETER_BIN_DIR=$(get_python_exec_prefix)
 fi
 
 # cleanup_ceilometer() - Remove residual data files, anything left over from previous