Part of 28863.

Part of 28863.

Part of 28863.

Part of 28863.

Part of 28863.

Part of 28863.

Part of 28863.

Part of 28863.

But do replacements for decoding errors.

Part of 28863.

Part of 28863.

Part of 28863.

Part of 28863.

Rather than just printing "None".

Part of 28863.

Some relays are unreliable, but we still want the tests to check
the different types of relays.

Part of 28863.

And move a comment.

Part of 28863.

Part of 28863.

But maintain compatibility with older stem versions.

Part of 28863.

Comment-only change.

Part of 28863.

Part of 28863.

This change makes it easier to run the travis tests locally.

Part of 28863.

Part of 32632 and 28863.

Part of 28863.

Part of 28863.

Part of 28863.

Part of 28863.

Use Xenial for pypy.

Part of 32632 and 28863.

Use Ubuntu Bionic and macOS 10.14.

Install Homebrew python@2 in macOS
macOS needs pip(2) to install fallback scripts dependencies.

Part of 32632 and 28863.

* Restrict the valid True and False bool values
* use default for unset env var, and (not default) for empty set env var

Closes 31305.

Part of 31305.

Also add a requirements.txt

Initial implementation of #28979.

Tested with:
TOR_FB_ONIONOO_LIMIT=200 ./updateFallbackDirs.py

Part of 29100.

Tested with:
$ TOR_FB_MAX_FALLBACK_COUNT=10 ./updateFallbackDirs.py check_existing
$ TOR_FB_MODE=check_existing TOR_FB_MAX_FALLBACK_COUNT=10 ./updateFallbackDirs.py

Part of 29100.

Tested using:
$ TOR_FB_MAX_FALLBACK_COUNT=10 ./updateFallbackDirs.py

Part of #29100.

And remove a duplicate "import re".

Part of 29100.