add support for two storage pools - nixinit-volumes and nixinit-iso
remove vol from above storage pool when deleting instance
remove iso from storage pool when deleting instance
this PR now enables a much simpler flow of creating a bootstrap, listing bootstraps and removing them and the main parts are cleaned up such that it can simply be run all over again.
Modifications:
nixinit-volumes
andnixinit-iso
Closes #5.