should run `apt` and `dpkg` entirely jailed inside the virtualenv

[attilammagyar]

Just a note before I completely forget it:

It would be cleaner to get apt and dpkg not to use any global state. As we've already found out, apt can be told to manage some of its state and configuration from customized files and directories, e.g.:

apt-get \
    -o 'Dir::Etc::SourceList=...' \
    -o 'Dir::Etc::SourceParts=...' \
    -o 'Dir::Etc::Main=...' \
    -o 'Dir::Etc::Parts=...' \
    -o 'Dir::Etc::Preferences=...' \
    -o 'Dir::Etc::PreferencesParts=...' \
    -o 'Dir::State::Lists=...' \
    -o 'Dir::Cache::Archives=...' \
    -o 'Debug::NoLocking=1' \
    --allow-unauthenticated \
    --yes \
        install ...

The problem is if apt runs dpkg without passing a --root option. We might be able to workaround that by putting a wrapper inside the virtualenv's bin directory with the name dpkg which would invoke the real dpkg with passing the required options.

[nyirog]

The Action.popen shoud be extended to handle extra aliases, instead of the PATH workaround.
By the way we don't use any command from the virtuaenv right now.