[autodiscovery] annotations with multi instances bug

[CharlyF]

What does this PR do?

Bug fix of #3341

Annotations with multi instances configuration leads to check level tags be added to the container level tags array.

While adding container tags with this method, performs a shallow copy of the container tag array to avoid adding tags from the previous instance ( which would come from this for loop), contains its check tags.

Motivation

Issue encountered by a customer.

Testing Guidelines

Instantiate a pod with annotations containing several instances (along the lines of this example)
The agent will detect the check but it will add the config level tags to the container level ones.
e.g.:

 (u'num.empl',
  1503048087,
  300024.0,
  {'hostname': 'i-0xxx',
   'tags': [u'kube_deployment:repl',
            u'kube_namespace:default',
            u'kube_replica_set:repl',
            u'env:prd',
            u'dbinstanceidentifier:dbi2',
            u'name:mysql',
            u'account:analytics',
            u'dbinstanceidentifier:dbi',
            u'team:data',
            u'image_tag:3.0',
            u'docker_image:gcr.io/google_containers/pause-amd64:3.0',
            u'image_name:gcr.io/google_containers/pause-amd64',
            u'table:playcount',
            u'dbinstanceidentifier:dbi2',
            u'env:prd',
            u'account:analytics',
            u'team:data'],
   'type': 'gauge'}),

As per the above pod yaml, this metric should only be tagged with dbinstanceidentifier:dbi2.
With the change, we have:

 (u'num.empl',
  1503050652,
  300024.0,
  {'hostname': 'i-0xxx',
   'tags': [u'kube_deployment:repl',
            u'kube_namespace:default',
            u'kube_replica_set:repl',
            u'env:prd',
            u'dbinstanceidentifier:dbi2',
            u'name:mysql',
            u'account:analytics',
            u'team:data',
            u'image_tag:3.0',
            u'docker_image:gcr.io/google_containers/pause-amd64:3.0',
            u'image_name:gcr.io/google_containers/pause-amd64',
            u'table:playcount',
            u'dbinstanceidentifier:dbi2',
            u'env:prd',
            u'account:analytics',
            u'team:data'],
   'type': 'gauge'}),

[hkaj]

Good catch! Thanks for digging in this issue.

If that's the only place we use it I'd rather not import copy and do tags = c_tags[:] instead. It will create a new list with all the elements of c_tags.

[aerostitch]

Tested with @hkaj's suggestion and it fixed the issue I had with way too much tags on my "query" metrics for the mysql integration configured in multi-instances mode via k8s annotations.

[hkaj]

what about this?

def _fill_tpl(self, state, c_id, instance_tpl, variables, c_tags=[]):
    ...
    tags = c_tags[:]

[hkaj]

👌