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/cinder b/lib/cinder
index 5f4f979..28b3caa 100644
--- a/lib/cinder
+++ b/lib/cinder
@@ -47,7 +47,7 @@
 if [[ -d $CINDER_DIR/bin ]]; then
     CINDER_BIN_DIR=$CINDER_DIR/bin
 else
-    CINDER_BIN_DIR=/usr/local/bin
+    CINDER_BIN_DIR=$(get_python_exec_prefix)
 fi
 
 # Name of the lvm volume group to use/create for iscsi volumes