conf: improve logging configuration

- both "error_log()" and "access_log()" now support "syslog:" prefix
- "error_log()" supports "stderr" destination
- both "error_log()" and "access_log()" now support "off" destination (with minor notes for "error_log()")

angie/autoconf/core-error-log.conf.j2

@@ -1,4 +1,3 @@
-{%- import 'snip/log.j2mod' as ngx_log -%}
-
-{# {{ ngx_log.error_log(dest='error.log', level=env.NGX_LOGLEVEL) }} #}
-{{ ngx_log.error_log(level=env.NGX_LOGLEVEL) }}
+{%- import 'snip/log.j2mod' as _log -%}
+{#- {{ _log.error_log(dest='error.log', level=env.NGX_LOGLEVEL) }} -#}
+{{ _log.error_log(level=env.NGX_LOGLEVEL) }}

angie/autoconf/http-access-log/default.conf.j2

@@ -1,4 +1,3 @@
-{%- import 'snip/log.j2mod' as ngx_log -%}
-
-{# {{ ngx_log.access_log(dest='access.log', format='main') }} #}
-{{ ngx_log.access_log(format='main') }}
+{%- import 'snip/log.j2mod' as _log -%}
+{#- {{ _log.access_log(dest='access.log', format='main') }} -#}
+{{ _log.access_log(format='main') }}

angie/snip/log.j2mod

@@ -1,12 +1,35 @@
-{%- macro error_log(dest='error.log', level='warn') %}
-error_log  {{ '/run/ngx/log'|join_prefix(dest) | ngx_esc }}  {{ level | ngx_esc }};
-{%- endmacro %}
+{% macro error_log(dest='error.log', level='warn') %}
+  {%- if dest == 'off' %}
+## not a really disabled log but quiet as less as possible
+error_log stderr emerg;
+  {%- else %}
+error_log
+    {%- if dest == 'stderr' %}
+  {{ dest }}
+    {%- elif dest.startswith('syslog:') %}
+  {{ dest | ngx_esc }}
+    {%- else %}
+  {{ join_prefix('/run/ngx/log', dest) | ngx_esc }}
+    {%- endif %}
+  {{ level | ngx_esc }};
+  {%- endif %}
+{% endmacro %}
 
 
-{%- macro access_log(dest='access.log', format='main') %}
-access_log  {{ '/run/ngx/log'|join_prefix(dest) | ngx_esc }}  {{ format | ngx_esc }}
+{% macro access_log(dest='access.log', format='main') %}
+  {%- if dest == 'off' %}
+access_log off;
+  {%- else %}
+access_log
+    {%- if dest.startswith('syslog:') %}
+  {{ dest | ngx_esc }}
+    {%- else %}
+  {{ join_prefix('/run/ngx/log', dest) | ngx_esc }}
+    {%- endif %}
+  {{ format | ngx_esc }}
     {%- for k, v in kwargs|dictsort %}
   {{ "{}={}".format(k, v) | ngx_esc }}
     {%- endfor %}
 ;
-{%- endmacro %}
+  {%- endif %}
+{% endmacro %}