rhel: Fix reload of OVS_USER_ID on startup.

rhel: Fix reload of OVS_USER_ID on startup.

OVS_USER_ID was being picked up from a previously existing
openvswitch.useropts rendering innefective any configuration change
through sysconfig.

There is no ordering between Exec* and Environment* stanzas of systemd,
full Enviroment* is always loaded before each Exec*. We make
sure that openvswitch.useropts is removed in a first Exec so that a
fresh OVS_USER_ID can be picked up from config in successive Exec*.

Fixes: 94e1e8b ("rhel: run ovn with the same user as ovs")
Signed-off-by: Jaime Caamaño Ruiz <jcaamano@suse.com>
Acked-by: Greg Rose <gvrose8192@gmail.com>
Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>