Added check to consul.yaml.erb for 'tags:'

[grogancolin]

I noticed when you don't pass a tag to
default['datadog']['consul']['instances'], it prints an empty tags section.

instances:
  - url: http://127.0.0.1:8500
    new_leader_checks: false
    catalog_checks: true
    service_whitelist: []
    tags:

This messes up with this line in the check.

The consul check is then failing with

2017-10-11 10:52:32 UTC | ERROR | dd.collector | checks.consul(__init__.py:814) | Check 'consul' instance #0 failed
Traceback (most recent call last):
  File "/opt/datadog-agent/agent/checks/__init__.py", line 797, in run
    self.check(copy.deepcopy(instance))
  File "/opt/datadog-agent/agent/checks.d/consul.py", line 240, in check
    for tag in instance.get('tags', []):
TypeError: 'NoneType' object is not iterable

This adds an extra check to the template so it also checks if the 'tags' section actually has elements.

[olivielpeau]

👌 Good catch @grogancolin, thanks!