attempt to fix issue with token not being read

[mindw]

A recent change introduced a regressions - The cloudwatch log groups are re-read due to issues with token handling. It seems the cloud watch token read != write most likely introduced in #215.

This is by no means a mergeable PR - my ruby skills are non-existant.

config:

<source>
  @id cloudwatch_logs_cloudhsm
  @type cloudwatch_logs
  log_group_name /aws/cloudhsm/<reducted>
  log_stream_name hsm
  use_log_stream_name_prefix true

  region "#{ENV['AWS_REGION']}"

  <storage>
    @type local
    persistent true
  </storage>

  <parse>
    @type none
    message_key log
  </parse>
  tag cloudwatch_logs.cloudhsm
  include_metadata true
</source>

Thank you all for supporting and maintaining this great plugin :)

[cosmo0920]

Sorry for to be late to merge this. Just merged.