Add fedora/el-7 systemd support

This updates the packaging and adds a systemd service file
and supporting files to support systemd on Fedora >= 18 and
EL >= 7.

In addition to the razor-server.service file itself, the
razor-server-tmpfiles.conf used the systemd tmpfiles.d
mechanism to ensure that the /run/razor-server
directory is created on boot with the proper ownership
as /run is now using tmpfs.

The /usr/share/razor-server/razor-server.env file
simply wraps up environment variables that were
being set in the init script in a form suitable
for systemd.
Spec tests for `razor events`

This adds tests for the `razor events` query.

For https://tickets.puppetlabs.com/browse/RAZOR-382
Limit results from `razor events`

The list of events in `razor events` can grow unwieldy very quickly. This
change instates a default of 20 rows returned with options to return
different rows using parameters /api/collections/events:
- `limit` determines the maximum number of rows to return,
which defaults to 20.
- `start` determines what row number to start with, which defaults to 0.
- `all` (boolean; 1 or 'true' etc.) returns all rows in the dataset.

Fixes https://tickets.puppetlabs.com/browse/RAZOR-382