ntp: sync ebuild with upstream

We were missing `Conflicts=systemd-timesyncd.service` which has been
added to the upstream ebuild. A few other minor tweaks but nothing big.
ntp: bump to 4.2.8, includes important security fixes

This release includes some important security updates:
http://www.kb.cert.org/vuls/id/852879

Also, support for the ntpdc client in ntpd has been removed upstream.
The ntpq client must be used instead.
ntp: sync updates from upstream, replace 'examples' use flag with 'perl'

Some minor updates from upstream such as a fix for building without
openssl which doesn't impact our current configuration. Additionally,
our 'examples' use flag was non-functional because 4.2.8 now includes
scripts in its normal build system and installs them to bin. Instead add
a better named 'perl' use flag and patch the build.
ntp: update Manifest
Merge pull request #1026 from marineam/ntp

NTP 4.2.8 for build-522