[sonic-package-manager] Use tag to start application

This is done in order to be able to start using tag which will provide a user-friendly identifier when running docker ps.

Author: DavidZagury

files/build_templates/docker_image_ctl.j2

@@ -744,6 +744,8 @@ start() {
 {%- if docker_container_name == "gbsyncd" %}
         -v /var/run/docker-syncd$DEV:/var/run/sswsyncd \
         "docker-$GBSYNCD_PLATFORM":latest \
+{%- elif docker_image_tag is defined and docker_image_tag is not none %}
+        {{docker_image_tag}} \
 {%- elif docker_image_name is defined %}
         {{docker_image_name}}:latest \
 {%- else %}