fix fast reboot compatibility (#3083)

* fix fast reboot compatibility

We should handle both cases for backward-compatible with 201803:
 - fast-reboot
 - SONIC_BOOT_TYPE=fast-reboot

* handle review comments
* add a comment that getBootType code snippet is shared between two files

files/build_templates/docker_image_ctl.j2

@@ -134,6 +134,9 @@ start() {
     echo "Creating new {{docker_container_name}} container"
 {%- else %}
     echo "Creating new {{docker_container_name}} container with HWSKU $HWSKU"
+{%- endif %}
+{%- if sonic_asic_platform == "mellanox" %}
+    # TODO: Mellanox will remove the --tmpfs exception after SDK socket path changed in new SDK version
 {%- endif %}
     docker create {{docker_image_run_opt}} \
 {%- if '--log-driver=json-file' in docker_image_run_opt or '--log-driver' not in docker_image_run_opt %}