Optional postgres server/address tags

[verterok]

Hi,

This PR adds an address_tag (boolean) option to the postgresql input, to configure if the server tag is created or not.
Default is current behavior where server tag is created.

My main usecase is to get cleaner graphite metric namespace. for example:
current ns: {prefix}.{host}.postgresql.dbname}.host=10_25_238_72_user=db_39_telegraf_dbname=telegraf.blks_read
with address_tag=false: {prefix}.storage-db-0.postgresql.{dbname}.blks_read

[sparrc]

thanks for the contribution @verterok, but with PR #1017 we will have the ability to generically remove remove tags from all input/output plugins. So I'm going to close in favor of that.

[verterok]

That's pretty cool and way more elegant than my approach.
thanks!