download-dependencies: merge into ./build --download-dependencies

Reuses the module system dependencies present there.

run: make --dry-run work even when there is no out directory yet

docker: make the wrapping more intuitive

.travis.yml

@@ -2,20 +2,10 @@ language: cpp
 
 sudo: required
 
-install: |
-  cd "$TRAVIS_BUILD_DIR"
-  bash -x ./download-dependencies --travis
-
 script: |
   cd "$TRAVIS_BUILD_DIR"
-  # --nproc: I'm unable to install nproc on Travis.
-  # TODO why? Is part of coreutils in Ubuntu 16.04:
-  # http://manpages.ubuntu.com/manpages/trusty/man1/nproc.1.html
-  # which ./download-dependencies is installing.
-  #
   # awk: without it, too much stdout (4Mb max)
   # If we ignore stdout: Travis kills job because it spent
   # too long without any new stdout.
-  bash -x ./build-qemu --nproc 16 |& awk 'NR % 1000 == 0'
-  bash -x ./build-buildroot --nproc 16 |& awk 'NR % 1000 == 0'
+  bash -x ./build --download-dependencies --travis |& awk 'NR % 1000 == 0'
   bash -x ./run --kernel-cli 'init=/poweroff.out'