replace celery task decorators with a kombu-based publisher

this commit implements the bulk of `awx-manage run_dispatcher`, a new
command that binds to RabbitMQ via kombu and balances messages across
a pool of workers that are similar to celeryd workers in spirit.
Specifically, this includes:

- a new decorator, `awx.main.dispatch.task`, which can be used to
  decorate functions or classes so that they can be designated as
  "Tasks"
- support for fanout/broadcast tasks (at this point in time, only
  `conf.Setting` memcached flushes use this functionality)
- support for job reaping
- support for success/failure hooks for job runs (i.e.,
  `handle_work_success` and `handle_work_error`)
- support for auto scaling worker pool that scale processes up and down
  on demand
- minimal support for RPC, such as status checks and pool recycle/reload

installer/roles/image_build/files/supervisor_task.conf

@@ -2,8 +2,8 @@
 nodaemon = True
 umask = 022
 
-[program:celery]
-command = /var/lib/awx/venv/awx/bin/celery worker -A awx -B -l debug --autoscale=50,4 -Ofair -s /var/lib/awx/beat.db -n celery@%(ENV_HOSTNAME)s
+[program:dispatcher]
+command = awx-manage run_dispatcher
 directory = /var/lib/awx
 environment = LANGUAGE="en_US.UTF-8",LANG="en_US.UTF-8",LC_ALL="en_US.UTF-8",LC_CTYPE="en_US.UTF-8"
 #user = {{ aw_user }}
@@ -15,18 +15,6 @@ stdout_logfile_maxbytes=0
 stderr_logfile=/dev/stderr
 stderr_logfile_maxbytes=0
 
-[program:celery-watcher]
-command = /usr/bin/awx-manage watch_celery
-directory = /var/lib/awx
-environment = LANGUAGE="en_US.UTF-8",LANG="en_US.UTF-8",LC_ALL="en_US.UTF-8",LC_CTYPE="en_US.UTF-8"
-autostart = true
-autorestart = true
-stopwaitsecs = 5
-stdout_logfile=/dev/stdout
-stdout_logfile_maxbytes=0
-stderr_logfile=/dev/stderr
-stderr_logfile_maxbytes=0
-
 [program:callback-receiver]
 command = awx-manage run_callback_receiver
 directory = /var/lib/awx
@@ -50,7 +38,7 @@ stderr_logfile=/dev/stderr
 stderr_logfile_maxbytes=0
 
 [group:tower-processes]
-programs=celery,celery-watcher,callback-receiver,channels-worker
+programs=dispatcher,callback-receiver,channels-worker
 priority=5
 
 # TODO: Exit Handler

installer/roles/image_build/templates/Dockerfile.j2

@@ -41,6 +41,7 @@ RUN yum -y install epel-release && \
     rm -rf /root/.cache
 
 RUN mkdir -p /var/log/tower
+RUN chmod -R g+w /var/log/tower
 RUN mkdir -p /etc/tower
 COPY {{ awx_sdist_file }} /tmp/{{ awx_sdist_file }}
 RUN OFFICIAL=yes pip install /tmp/{{ awx_sdist_file }}