Spec for HAPROXYHTTP pattern.

We ran into parsing problems with this pattern and my first step was to
look at the tests. There were none so I took the apache log example and
adapted it for haproxy using the haproxy documentation format as the
example log string.

HELP! I am not sure why using date { timestamp =>
"dd/MMM/YYYY:HH:mm:ss.S" } doesn't set the event timestamp correctly so
the example uses mutate but at least passes.
Use date filter to set the timestamp from the haproxy accept_date
Remove date filter from haproxy parsing example.
Merge pull request #469 from wesmaldonado/spec_for_parse_haproxy_log_example

Added spec for HAPROXYHTTP pattern.