perform install_infra sooner in stack.sh

The install_infra() call needs to be done earlier since
pip_install_gr() depends on it. Also the fact that python module names
are supposed to be lower case but some use camel case is a problem
(for example with XenAPI).

Change-Id: I7012d77134fa0d9c746d87e837934e7dcb337e5c
Closes-Bug: #1441820
diff --git a/stack.sh b/stack.sh
index 69b76a9..9ecc49c 100755
--- a/stack.sh
+++ b/stack.sh
@@ -714,6 +714,9 @@
 # Extras Pre-install
 # ------------------
 
+# Install required infra support libraries
+install_infra
+
 # Phase: pre-install
 run_phase stack pre-install
 
@@ -733,9 +736,6 @@
 
 echo_summary "Installing OpenStack project source"
 
-# Install required infra support libraries
-install_infra
-
 # Install Oslo libraries
 install_oslo