Fetch vars for host directly when calculating the delegated user

This fixes the case in which the delegated to host may not be in the
specified hosts list, in which cases facts/vars for the host were
not available in the injected hostvars.

This also fixes the inventory variable fetching function, so that an
unknown host raises a proper error as opposed to a NoneType exception.

Fixes #8224

lib/ansible/inventory/__init__.py

@@ -437,7 +437,10 @@ class Inventory(object):
 
     def get_variables(self, hostname, update_cached=False, vault_password=None):
 
-        return self.get_host(hostname).get_variables()
+        host = self.get_host(hostname)
+        if not host:
+            raise Exception("host not found: %s" % hostname)
+        return host.get_variables()
 
     def get_host_variables(self, hostname, update_cached=False, vault_password=None):
 

lib/ansible/runner/__init__.py

@@ -367,6 +367,16 @@ class Runner(object):
             if inject['hostvars'][host].get('ansible_ssh_user'):
                 # user for delegate host in inventory
                 thisuser = inject['hostvars'][host].get('ansible_ssh_user')
+        else:
+            # look up the variables for the host directly from inventory
+            try:
+                host_vars = self.inventory.get_variables(host, vault_password=self.vault_pass)
+                if 'ansible_ssh_user' in host_vars:
+                    thisuser = host_vars['ansible_ssh_user']
+            except Exception, e:
+                # the hostname was not found in the inventory, so
+                # we just ignore this and try the next method
+                pass
 
         if thisuser is None and self.remote_user:
             # user defined by play/runner