Your nova.conf works for me. nova-compute starts successfully with your nova.conf.
Do you still fail to start nova-compute with this conf?
If I enabled the line network_manager in nova.conf, I got the same error as yours:
2012-10-09 02:03:18 INFO nova.compute.manager [-] Loading compute driver 'libvirt.LibvirtDriver'
2012-10-09 02:03:18 CRITICAL nova [-] No module named quantum.manager
P.S.
I tested with git version. I tried the ubuntu package version later.
Your nova.conf works for me. nova-compute starts successfully with your nova.conf.
Do you still fail to start nova-compute with this conf?
If I enabled the line network_manager in nova.conf, I got the same error as yours: manager [-] Loading compute driver 'libvirt. LibvirtDriver'
2012-10-09 02:03:18 INFO nova.compute.
2012-10-09 02:03:18 CRITICAL nova [-] No module named quantum.manager
P.S.
I tested with git version. I tried the ubuntu package version later.