The MySQL DB driver has it's own DSN parsing function. Previously we
were using the url.Parse function, but this causes problems because a
valid MySQL DSN can be an invalid http URL, namely when using some
special characters in the password.

This change uses the MySQL DB driver's builtin ParseDSN function and
applies a timeout parameter natively via that.

Another benefit of this change is that we fail earlier if given an
invalid MySQL DSN.

closes #870
closes #1842

closes #1344

closes #1771

allows for easier addition of a sliding window at a later time.

Also makes `period` be a generic argument for all aggregator plugins.

closes #1726

closes #1886

This was introducing a regression with influxdb output, leading to
collision an points missing.
This reverts commit 53f40063.

closes #1724
closes #1796

Previously, the graphite parser would simply overwrite any template that
had an identical filter to a previous template. This included the empty
filter.

Now we will still overwrite, but first we will sort to make sure that
the most "specific" template always matches.

closes #1731

closes #1793

Fixed json serialization to make sure only value type supported by OpenTSDB are sent and made sure we send numbers un-quoted event though OpenTSDB API accepts them as this is not clean json.

closes #1700

Map holding expected results was defined in multiple places, making test
cases a bit hard to read. This way we can change our expectations of
good results in one place and have them affect multiple test cases.

This behaviour was introduced along with socket support, but never got
documented properly.

Added a standard example for collecting interface metrics from switches or routers and tagging them properly.

closes #1666

fixes #1810

closes #1861

Let's align to InfluxDB 1.0 logging policy and log to systemd journal by
default.

closes #1732

Issue #1854