rust-vmm-ci: update it to run unittests priviliged

rust-vmm/rust-vmm-ci#165 allows us to
run unittests in a privileged container, so we can use AF_VSOCK
in our CI which was otherwise not allowed by docker.
This was already enabled for coverage tests.

Signed-off-by: Stefano Garzarella <[email protected]>

Author: stefano-garzarella