Fix cephx key rotation race condition with Nova

When new nova-compute units are added to Ceph-backed clouds,
cephx keys are temporarily reverted back to the wrong (old)
key value. This happens due to a race condition between the
client hooks of nova-compute and ceph-mon. Details can be
found in LP#2125295.

This patch ensures that nova-compute sends the application
name value early on to ensure the race condition does not
occur.

Closes-Bug: #2125295
Change-Id: Ibdd5ccdd6d26b5d72dd80ed54bd90b38d5c99ceb
Signed-off-by: Alejandro Santoyo <alejandro.santoyo@canonical.com>

hooks/nova_compute_hooks.py

@@ -479,6 +479,9 @@ def ironic_api_changed():
 @hooks.hook('ceph-relation-joined')
 @restart_on_change(restart_map())
 def ceph_joined():
+    # install old credentials first for backwards compatibility
+    send_application_name()
+
     pkgs = filter_installed_packages(['ceph-common'])
     if pkgs:
         status_set('maintenance', 'Installing ceph-common package')
@@ -486,8 +489,6 @@ def ceph_joined():
         # Bug 1427660
         if not is_unit_paused_set() and config('virt-type') in LIBVIRT_TYPES:
             service_restart(libvirt_daemon())
-    # install old credentials first for backwards compatibility
-    send_application_name()
 
 
 def get_ceph_request():