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/glance b/lib/glance
index 1c56a67..5d48129 100644
--- a/lib/glance
+++ b/lib/glance
@@ -44,7 +44,7 @@
 if [[ -d $GLANCE_DIR/bin ]]; then
     GLANCE_BIN_DIR=$GLANCE_DIR/bin
 else
-    GLANCE_BIN_DIR=/usr/local/bin
+    GLANCE_BIN_DIR=$(get_python_exec_prefix)
 fi
 
 # Glance connection info.  Note the port must be specified.