Updated centos/fedora/oracle templates to use `hostname` for DHCP_HOSTNAME in
/etc/sysconfig/network/ifcfg-eth0, so the container's host name is propagated
to the host's DHCP server (e.g. dnsmasq, which also acts as the DNS server).
This resolves lxc/lxd#756
Signed-off-by: Lenz Grimmer <lenz@grimmer.com>