import: Call create_system_user_groups_for_realm outside the function.
import: Call create_system_user_groups_for_realm outside the function.

Previously, we had a function named create_add_users_to_system_user_groups
for creating system user groups and adding users to them in case when
exports do not contain these groups when importing from other services.

This commit just separates out the call to create_system_user_groups_for_realm
outside the function and the function is thus renamed to
add_users_to_system_user_group. This change is done because in further
commits we would need to update the import order and user groups will
be created before creating user profile objects.

andersk/zulip,andersk/zulip,andersk/zulip,rht/zulip,andersk/zulip,andersk/zulip,zulip/zulip,zulip/zulip,zulip/zulip,rht/zulip,zulip/zulip,zulip/zulip,rht/zulip,rht/zulip,andersk/zulip,zulip/zulip,rht/zulip,zulip/zulip,andersk/zulip,rht/zulip,rht/zulip