Uhyve is not "reentrant" / can't create two vms in the same process

[jounathaen]

This is, because upon the creation of a new VM, KVM gets initialized which results in a panic.

We want this, to have multiple tests in a single integration test file.

CC: @n0toose

[n0toose]

Note: To reproduce this, add two tests sequentially in the test-kernels (by copying and pasting the same test with a different name) and run cargo test --test serial -- --nocapture (or replace serial with another test).