As of I3629b84d3255a8fe9d8a7cea8c6131d7c40899e8 nova
now requires the service_user section to be configured
to address CVE-2023-2088. This change adds
the service user section to the nova.conf template in
the nova and nova-cell roles.

Related-Bug: #2004555
Signed-off-by: Sven Kieske <kieske@osism.tech>
Change-Id: I2189dafca070accfd8efcd4b8cc4221c6decdc9f
(cherry picked from commit a77ea13ef1991543df29b7eea14b1f91ef26f858)
(cherry picked from commit 03c12abbcc107bfec451f4558bc97d14facae01c)
(cherry picked from commit cb105dc293ff1cdb11ab63fa3e3bf39fd17e0ee0)
(cherry picked from commit efe6650d09441b02cf93738a94a59723d84c5b19)