nixos/tests/virtualbox: Don't parallelize VM boot.

I'm not quite sure why the official Hydra gets a kernel panic in one of
two VMs using the exact same kernels:

https://hydra.nixos.org/build/26339384

Because the kernel panic happens before stage 1, let's wait for the
first VM to boot up and after the bootup is done, start the second one
in hope that it won't trigger the panic.

Oddly enough, whenever I run the test on my own Hydra and on my local
machines, I don't get anything like that.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

aszlig baf1d1dc 000a2108

Changed files
+1 -2
nixos
+1 -2
nixos/tests/virtualbox.nix
···
vbm("startvm test1");
waitForStartup_test1;
vbm("startvm test2");
waitForStartup_test2;
-
-
waitForVMBoot_test1;
waitForVMBoot_test2;
$machine->screenshot("net_booted");
···
vbm("startvm test1");
waitForStartup_test1;
+
waitForVMBoot_test1;
vbm("startvm test2");
waitForStartup_test2;
waitForVMBoot_test2;
$machine->screenshot("net_booted");