* Bring back colors on Travis, which was disabled since #39036.
Append --color=always to cargo when running in CI environment.
* Removed `set -x` in the shell scripts. The `retry` function already
prints which command it is running, add `-x` just add noise to the
output.
* Support travis_fold/travis_time. Matching pairs of these allow Travis CI
to collapse the output in between. This greatly cut down the unnecessary
"successful" output one need to scroll through before finding the failed
statement.
This commit attempts to move more network operations to being retryable through
various operations. For example git submodule updates, downloading snapshots,
etc, are now all in retryable steps.
Hopefully this commit can cut down on the number of network failures we've been
seeing!
