Map /src & /debug for debug docker containers (#3470)

* Add debug docker for SNMP.

* Removed a redundant install of debug packages.
Propagate the debug flag to template file to mount /dbg & /src to debug containers.

* Revert the last change to retain the original

files/build_templates/docker_image_ctl.j2

@@ -139,6 +139,9 @@ start() {
     # TODO: Mellanox will remove the --tmpfs exception after SDK socket path changed in new SDK version
 {%- endif %}
     docker create {{docker_image_run_opt}} \
+{%- if install_debug_image == "y" %}
+        -v /src:/src:ro -v /debug:/debug:rw \
+{%- endif %}
 {%- if '--log-driver=json-file' in docker_image_run_opt or '--log-driver' not in docker_image_run_opt %}
         --log-opt max-size=2M --log-opt max-file=5 \
 {%- endif %}

slave.mk

@@ -581,6 +581,7 @@ $(addprefix $(TARGET_PATH)/, $(SONIC_INSTALLERS)) : $(TARGET_PATH)/% : \
 	export swsssdk_py2_wheel_path="$(addprefix $(PYTHON_WHEELS_PATH)/,$(SWSSSDK_PY2))"
 	export platform_common_py2_wheel_path="$(addprefix $(PYTHON_WHEELS_PATH)/,$(SONIC_PLATFORM_COMMON_PY2))"
 	export redis_dump_load_py2_wheel_path="$(addprefix $(PYTHON_WHEELS_PATH)/,$(REDIS_DUMP_LOAD_PY2))"
+	export install_debug_image="$(INSTALL_DEBUG_TOOLS)"
 
 	$(foreach docker, $($*_DOCKERS),\
 		export docker_image="$(docker)"