Due to quite real problem of generating vast number of data series through
mesos tasks metrics this feature is disabled until better solution is found.

Tagging values by executor_id can create quite a lot data series
in InfluxDB so we should stick to framework_id and server.

closes #1137

closes #1517

max-repetitions = 10 is the default of net-snmp utils according to
http://net-snmp.sourceforge.net/docs/man/snmpbulkwalk.html

retries = 3 is the default of gosnmp:
https://godoc.org/github.com/soniah/gosnmp#pkg-variables

Could deal with some parts of the performance issues reported
by #1665

Also consolidated the translation code to obtain all info with just 1 command execution.

Also split test command mocks out to their own file for cleanliness.

closes #1752

closes #1751

The default is 0 so we hit a division by 0 error and crash. This checks
ensure we will not crash and `log` and continue to let telegraf run

Also we set default allow pending message number to 10000

* Allow numeric and non-string values for tag_keys.

According to the go documentation the JSON deserializer only produces these
base types in output:
- string
- bool
- float64
- nil
With this patch bool, float64 and nil values get converted to a string when
their field key is specified in tag_keys. Previously the field was simply
discarded.

* Updated handling of nil for passing tests.

The automated tests are less than trivial to reproduece locally for me,
so I hope CircleCI wonn't mind...

* Updated changelog entries with PR and issue links.

* Code correctly handles colons in tag values now

* Modified existing datadog tag test to include a tag value containing a colon

closes #1789

* Add container state metrics to docker plugin.

* Update changelog.

closes #1773

closes #1775

speed up statsd parser

add statsd parsing benchmarks

fixes #1764

closes #1530

closes #1728

closes #1733

closes #1738

* separate hello and authenticate functions, force connection close at end of write cycle so we don't hold open idle connections, which has the benefit of mostly removing the chance of getting hopelessly connection lost

* update changelog, though this will need to be updated again to merge into telegraf master

* bump instrumental agent version

* fix test to deal with better better connect/reconnect logic and changed ident & auth handshake

* Update CHANGELOG.md

correct URL from instrumental fork to origin and put the change in the correct part of the file

* go fmt

* Split out Instrumental tests for invalid metric and value.

* Ensure nothing remains on the wire after final test.

* Force valid metric names by replacing invalid parts with underscores.

* Multiple invalid characters being joined into a single udnerscore.

* Adjust comment to what happens.

* undo split hello and auth commands, to reduce roundtrips

* Add ignored_databases option to postgresql configuration files, to enable easy filtering of system databases without needing to whitelist all the databases on the server.  Add tests for database whitelist and blacklist.

* run go fmt on new postgresql database whitelist/blacklist code

* add postgresql database blacklist option to changelog

* remove a bad merge from the changelog

also remove locking around adding metrics. Instead, keep a waitgroup on
the ServeHTTP function and wait for that to finish before returning from
the Stop() function

closes #1407

fix incredibly stupid bugs

populate README

support query endpoint and change default listen port

set response headers for query endpoint

add unit tests

revert erroneous Godeps change

add plugin ref to top-level README

remove debug output and add empty post body test

fix linter errors

move stoppableListener into repo

use constants for http status codes

add CHANGELOG entry

address code review comments re. style/structure

address further code review comments

add note to README re. database creation calls per PR comments