Fix: Create missing symlink

Error:
playbook_file: provision/devstack-centos.yaml is invalid: stat
provision/devstack-centos.yaml: no such file or directory

Signed-off-by: Anil Belur <abelur@linuxfoundation.org>
Change-Id: Ibe2156ddc28ee127df36ac42a4389a0e2f5c5432

diff --git a/provision/devstack-centos.yaml b/provision/devstack-centos.yaml
new file mode 120000 (symlink)
index 0000000..f0655ee
--- /dev/null
+++ b/provision/devstack-centos.yaml
@@ -0,0 +1 @@
+devstack.yaml
\ No newline at end of file