Properly filter for local admins emails

Originally the mail.local_administrators only returned users who
were members of the default builtin local administrators privilege
by virtue of auxiliary group membership. This commit makes the
logic more generic. Since the method was originally written we
expanded user.query output to include information about the
user's roles and so we can select all users with FULL_ADMIN
privileges (which may be granted by non-default privilege sets).

src/middlewared/middlewared/plugins/mail.py

@@ -492,11 +492,11 @@ def _from_addr(self, config):
 
     @private
     async def local_administrators_emails(self):
-        return list(set(
-            user["email"]
-            for user in await self.middleware.call("privilege.local_administrators")
-            if user["email"]
-        ))
+        return list(set(user["email"] for user in await self.middleware.call("user.query", [
+            ["roles", "rin", "FULL_ADMIN"],
+            ["local", "=", True],
+            ["email", "!=", None]
+        ])))
 
     @private
     async def local_administrator_email(self):

tests/api2/test_mail_admins.py

@@ -0,0 +1,27 @@
+import pytest
+
+from middlewared.test.integration.assets.account import user
+from middlewared.test.integration.utils import call
+
+MAILUSER = 'wilbur'
+MAILADDR = '[email protected]'
+PASSWD = 'abcd1234'
+
+
+@pytest.fixture(scope='module')
+def full_admin_user():
+    ba_id = call('group.query', [['gid', '=', 544]], {'get': True})['id']
+    with user({
+        'username': MAILUSER,
+        'full_name': MAILUSER,
+        'group_create': False,
+        'email': '[email protected]',
+        'group': ba_id,
+        'password': PASSWD
+    }, get_instance=True) as u:
+        yield u
+
+
+def test_mail_administrators(full_admin_user):
+    emails = call('mail.local_administrators_emails')
+    assert MAILADDR in emails