Investigate test flake where ignite-spawn fails to add default route for VM net device

[stealthybox]

See CI for more details: https://weaveworks-foss.semaphoreci.com/jobs/5a909c1b-babc-4bf1-b3e4-aa43a9a113e2#L632/

=== RUN   TestCopyFileFromHostToVM/file-with-content00:36
    TestCopyFileFromHostToVM/file-with-content: cp_test.go:35: assertion failed: error is not nil: exit status 1: cmd: 00:36
        "/home/semaphore/ignite/bin/ignite run --name=e2e-test-copy-to-vm-file-with-content --ssh weaveworks/ignite-ubuntu"00:36
        time="2021-02-28T19:38:46Z" level=info msg="Created VM with ID \"15d29f5317073442\" and name \"e2e-test-copy-to-vm-file-with-content\""00:36
        time="2021-02-28T19:38:46Z" level=error msg="failed to setup network for namespace \"ignite-15d29f5317073442\": failed to add route '{0.0.0.0 00000000000000000000ffff00000000} via 10.61.0.1 dev eth0': network is unreachable"00:36
        time="2021-02-28T19:38:46Z" level=fatal msg="failed to add route '{0.0.0.0 00000000000000000000ffff00000000} via 10.61.0.1 dev eth0': network is unreachable"00:36
        00:36
    TestCopyFileFromHostToVM/file-with-content: cp_test.go:35: failed to run "/home/semaphore/ignite/bin/ignite run --name=e2e-test-copy-to-vm-file-with-content --ssh weaveworks/ignite-ubuntu": exit status 100:36
    TestCopyFileFromHostToVM/file-with-content: panic.go:617: assertion failed: error is not nil: exit status 1: cmd: 00:36
        "/home/semaphore/ignite/bin/ignite rm -f e2e-test-copy-to-vm-file-with-content"00:36
        time="2021-02-28T19:38:46Z" level=fatal msg="command [\"dmsetup\" \"remove\" \"--verifyudev\" \"ignite-15d29f5317073442\" \"ignite-15d29f5317073442-base\"] exited with \"device-mapper: remove ioctl on ignite-15d29f5317073442  failed: Device or resource busy\\nCommand failed\\n\": exit status 1"00:36
        00:36
    TestCopyFileFromHostToVM/file-with-content: panic.go:617: failed to run "/home/semaphore/ignite/bin/ignite rm -f e2e-test-copy-to-vm-file-with-content": exit status 100:43