(PUP-876) Skip resource service check on EL 6

Redmine issues (#4123) and (#4124) added acceptance tests on RHEL
systems to ensure that the services listed by chkconfig matched the list
of services returned by `puppet resource service`, but this assumed that
chkconfig would be authoritative for all running services. Commit
7bdcbea enabled the upstart service provider on EL 6 systems which
breaks this assumption and causes the acceptance tests to fail. This
commit disables these tests on EL 6 since the test is no longer
meaningful.
Merge pull request #2404 from adrienthebo/maint/master/pup-876-skip_resource_service_compare_on_redhat_6

(PUP-876) Skip resource service check on EL 6
(PUP-1839) Flush cache when setting value

The `set_value` method was deprecated and rewritten as part of the work
to implement `puppet config set`. However the new implementation lost
the call to `unsafe_clear_cache` which caused any set values to not show
up if the setting's value had previously been read. Also, the method was
still used by the `puppet device` code.

This is a small fix to get `puppet device` working again. This flushes
the cache and removes the deprecation.
Merge pull request #2409 from zaphod42/issue/master/pup-1839-incorrect-settings-when-using-puppet-device

(PUP-1839) Flush cache when setting value
Merge branch 'master' of https://github.com/puppetlabs/puppet