redhat: allow dpdk to also run as non-root user

redhat: allow dpdk to also run as non-root user

After this commit, users may start a dpdk-enabled ovs setup as a
non-root user.  This is accomplished by exporting the $HOME directory,
which dpdk uses to fill in it's semi-persistent RTE configuration.

This change may be a bit controversial since it modifies /dev/hugepages
as part of starting the ovs-vswitchd to set a hugetlbfs group
ownership.  This is used to enable writing to /dev/hugepages so that the
dpdk_init will successfully complete.  There is an alternate way of
accomplishing this - namely to initialize DPDK before dropping
privileges.  However, this would mean that if DPDK ever grows an uninit
/ reinit function, non-root ovs likely could never use it.

This does not change OvS+DPDK's SELinux requirements.  It still must be
disabled.

Signed-off-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Russell Bryant <russell@ovn.org>