Copy input directories to containers recursively

Earlier I've run a firefox-android build with RBM_VERBOSE_LOG=1.

I found that indeed we spend a very long time copying files. They are about 1600 files for slightly less than 500MB, so all this time is quite surprising.

My hypothesis is that it takes us this long time because we copy them one by one and we adjust their owner after each copy. I wonder if this adds a lot of overhead (we need to setup the container and chroot to it to run chown).

My proposal is that we first copy directories (such as the various gradle-dependencies-N) recursively, and that we apply the owner only at the end of the copy.