Draft: testing/ignite: new aport

Things that are still needed to consider/fix:

• ignited requires root privilege and containerd socket so I can't generate ignited.bash in build() (addressed by https://github.com/weaveworks/ignite/pull/955)
• Testing is welcome (the supported Firecracker version is 0.22.4 while we have 1.1.0)

From the list of requirements/dependencies I leave e2fsprogs, dmsetup and binutils as optional. This decision might need some judgements.