Have you verified with 'ps' that your nova-compute process is running with the same userid as the owner of /var/lib/nova

nova-compute is owned by nova, refer to the output below.
nova      3526     1  0 Dec10 ?        00:08:08 /usr/bin/python /usr/bin/nova-compute --logfile /var/log/nova/compute.log

/var/lib/nova is owned by nova, refer to the output below.
drwxr-xr-x. 10 nova       nova       4096 Dec 10 08:05 nova


 and /var/lib/nova/instances?
/var/lib/nova/instances/ is owned by nova refer to the out below
drwxr-xr-x. 4 nova nova   4096 Dec 11 01:42 instances

Is the directory /var/lib/nova/instances/5182d2ab-642d-45df-a362-48d9bda86371 getting created (that is, is the error specific to the file rather than the directory)?
the actual instance directory itself is NOT being created.


Are you out of disk
No
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg0-rootvol
                       35G  3.5G   30G  11% /
tmpfs                 1.9G  4.0K  1.9G   1% /dev/shm
/dev/sda1             485M   67M  393M  15% /boot
/dev/mapper/vg0-homevol
                      4.0G  137M  3.7G   4% /home
/dev/mapper/vg0-optvol
                      9.9G  247M  9.2G   3% /opt
/dev/mapper/vg0-tmpvol
                      4.0G  488M  3.3G  13% /tmp
/dev/mapper/vg0-varvol
                      7.9G  3.0G  4.6G  40% /var<----This will be a problem later but the image itself is a qcow that is thing provisioned. I don't believe this will precent it from launching
/dev/mapper/vg0-varlogvol
                      2.0G  352M  1.6G  19% /var/log
/dev/mapper/vg0-varlogauditvol
                      2.0G  125M  1.8G   7% /var/log/audit
/srv/loopback-device/swift_loopback
                      1.9G   67M  1.8G   4% /srv/node/swift_loopback