Make our build system more robust vs. apt-get transient errors

For instance, for build failures like

W: Failed to fetch http://ftp.us.debian.org/debian/dists/experimental/main/binary-i386/Packages  Hash Sum mismatch

E: Some index files failed to download. They have been ignored, or old ones used instead.
Fetched 43.1 MB in 19s (2224 kB/s)
P: Begin unmounting filesystems...

we should teach jenkins to detect them, and trigger a rebuild instead of notifying the responsible party of this (very often) meaningless error.

It would probably be even better to make our build system retry a few times (+ change mirrors, if any?) on such errors before giving up for real.

Feature Branch: feature/9430-build-system-vs-apt-transient-errors

Original created by @anonym on 9430 (Redmine)