We recently added a CDN in front of our CI mirrors as it's faster and
cheaper for us. This switches libc's CI to use it instead of accessing
the underlying bucket directly.
Previously mirrors were stored in the rust-lang-ci2 bucket, which is
meant to store temporary data (the CI artifacts). This switches the code
to fetch from the new mirrors bucket.
The old files won't be removed, but they won't be backed up either.
Specifically:
* Update the base docker images to ubuntu 16.10
* Update musl to version 1.1.15
This is necessary since the versions we were previously using do not
define CLONE_NEWCGROUP, so adding the symbol to the libc crate causes
test failures.
Yuki Okushi
oxalica
Pietro Albini
gnzlbg
Mateusz Mikuła
Tom Parker-Shemilt
Alex Crichton
Gabriel
Ian Denhardt