`apt-builder` actually expects a dependency package, rather than just manually installing the dependecies.  This is a bit of a legacy thing (and maybe not the greatest decision we made), but the usual path is to have a `debian/control` which contains a `Build-Depends` line, and run `mk-build-deps` which will generate a `projectname-build-deps_1.0_all.deb` package.  It then installs the package it finds.  (This make task is mainly used for things like adding repos that might be necessary to find those packages.)

Thankfully, `mk-build-deps` only needs the one `debian/control` file, and doesn't need/want the rest of the `debian/*` tree.  Could easily be done in a subdir, e.g. `cd mesos-deb-packaging && mk_build_deps && mv mesos_build_deps_1.0_all.deb ..`.

Also, I think you want `python-pip`.