Add service restart on package change

drop Ubuntu 14.04 support

Also convert template to `epp`.

Group them together and use puppet-strings tags to document them.
Previously, it was inconsistent with `cnf_socket` default in the class,
but all others in hiera.  This also meant it was not possible to group
them together in the parameter list without getting a puppet-lint
warning about optional parameters coming before required ones.

Accept `Sensitive` mysqld_exporter `cnf_password`

Support redis_exporter version >= 1.0.0

Allow users to override the default `alias` label which is set on the
exported scrape_jobs.

Add `scrape_job_labels` parameter to exporters

In systemd, the service is currently not being restarted after
configuration changes.  See GH-382

The acceptance test in this commit reconfigures prometheus with
the admin API enabled and then attempts to access it.

See https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-admin-apis

The [unreliable](https://puppet.com/docs/puppet/5.5/lang_defaults.html#behavior) resource default
```
File{
  notify => Class['prometheus::run_service']
}
```
is replaced by a `$notify` variable that is set on the relevant file
resources *and* `systemd::unit_file`.  Some care was needed to make sure
the reload behaviour wasn't broken.  ie If the configuration change is
just a new scrape job that is collected, the service should only be
reloaded, not restarted.

Fixes #382

Fix prometheus not restarting after config changes on systemd based systems

This wasn't done in the last major release due to time constraints and
`prometheus::redis_exporter` needing changes to support versions >=
1.0.0

Update default redis_exporter version to 1.3.4

This commit is a workaround for
https://tickets.puppetlabs.com/browse/PUP-10149

It can probably be reverted once 6.11.1 is out.

Workaround 6.11.0 systemd regression

Update default Prometheus version from 2.11.1 to 2.14.0

This reverts commit 943735d.

Release 8.0.0