Clean up acceptance spec helper

Puppet documentation states `unique` ("array merge") behavior
will return a merged array and will fail for hashes. We can
instead rework this lookup function to automatically lookup
the variables as per current best practises.

This change is in line with b188888.

Closes #536.

Not that many people know this is an option and can get confused
as to why their resources are missing bits and pieces that are
in fact defined in their Hiera sources. This should clear all of
that up.

More details and explanatory examples in use for `lookup_options`.

Based on further request in PR.

allow puppetlabs/inifile 4.x

Do a `deep` merge on `fpm` lookup

Fix os::family name for Debian.

Fix running apt update on Debian family

modulesync 2.12.0 and drop puppet 4

add ability to define composer update channel

delete legacy travis directory

add pool_purge option to init.pp

As of 2018-03-08, pear is flavored/prefixed in FreeBSD[1]. Remove the
special handling and use the configured prefix as for most other
distributions.

[1] See UPDATING note e.g. on https://www.freshports.org/devel/pear/

If the php version has been set in globals, use it to determine the
default package prefix on FreeBSD.
This should be a compatible change, since the package prefix can still
be overridden, and has to match the selected version anyway.

Improve package prefix selection on FreeBSD

Fix enabling of zend extensions