Replace erlang cookie fact with type and provider

Keeping secrets as facts is a potential security risk since facts
are generally not protected as secrets. This change removes the
rabbitmq_erlang_cookie fact. In order to make this feasible, the
exec that wipes out the rabbitmq db and the file resource managing
the cookie are replaced by a type and provider to reproduce this
functionality.
Stop setting a default cookie

Like passwords, secret cookies shouldn't have defaults. This
change removes the default and hard fails when a value is needed and
not set.
Update README
Merge pull request #282 from cmurphy/cookie

Replace erlang cookie fact with type and provider
Remove deprecated parameters

All parameters removed in this patch were deprecated prior to
3.0.0. It is time to let them go.
Stop claiming to support Puppet 2.7.
Merge pull request #284 from cmurphy/remove_deprecations

Remove deprecated parameters
Merge pull request #285 from cmurphy/rm_27

Stop claiming to support Puppet 2.7.
Prepare 5.0.0 release
Merge pull request #286 from cmurphy/release

Prepare 5.0.0 release