fix(net-misc/tlsdate): use the coreos fork

the chromium os fork works and there are some problems upstream I need
to work thorugh. Use this.
fix(net-misc/tlsdate): use econf on 9999 too
fix(net-misc/tlsdate): use service file from ebuild
chore(net-misc/tlsdate): fixup the comments related to user
fix(net-misc/tlsdate): ensure systemd eclass is used
chore(net-misc/tlsdate): sync 9999 ebuild
Merge pull request #245 from philips/add-tlsdate

fix(net-misc/tlsdate): use the coreos fork