Miscellaneous changes for CI, Docker and compiletest.
This PR contains 7 independent commits that improves interaction with CI, Docker and compiletest.
1. a4e5c91cb8 — Forces a newline every 100 dots when testing in quiet mode. Prevents spurious timeouts when abusing the CI to test Android jobs.
2. 1b5aaf22e8 — Use vault.centos.org for dist-powerpc64le-linux, see #45744.
3. 33400fbbcd — Modify `src/ci/docker/run.sh` so that the docker images can be run from Docker Toolbox for Windows on Windows 7. I haven't checked the behavior of the newer Docker for Windows on Windows 10. Also, "can run" does not mean all the test can pass successfully (the UDP tests failed last time I checked)
4. d517668a08 — Don't emit a real warning the linker segfault, which affects UI tests like https://github.com/rust-lang/rust/pull/45489#issuecomment-340134944. Log it instead.
5. 51e2247948 — During run-pass, trim the output if stdout/stderr exceeds 416 KB (top 160 KB + bottom 256 KB). This is an attempt to avoid spurious failures like https://github.com/rust-lang/rust/pull/45384#issuecomment-341755788
6. 9cfdabaf3c — Force `gem update --system` before deploy. This is an attempt to prevent spurious error #44159.
7. eee10cc482 — Tries to print the crash log on macOS on failure. This is an attempt to debug #45230.
2c4a0a78b8