Add instructions for adding/removing/updating users on
build-sunet-a.torproject.net as well as installing new packages.

We also update the tbb-team role to make it possible to remove users.

While updating the README file we also add a link for more details about
setting up a new nightly build machine.

When creating update responses for nightly builds, we don't want to
create a downloads.json file, so we make that optional.

Update testsuite_git_commit so that incremental mars are generated
as part of our nightly builds.

In rbm.conf we currently have var/max_torbrowser_incremental_from set to
2. In order to be able to generate incrementals from the previous two
versions, we need to keep 3 builds.

To make generation of incremental mars easier, we use the version as the
directory name (instead of just the date).

We also define the tbb_version option, which is used to set the
TORBROWSER_NIGHTLY_VERSION environment variable.

Previously we were using the prune-old-builds script which was located
in the testsuite repository in tools/prune-old-builds, as a git submodule.

As this script is not used anywhere other than here, it doesn't make
much sense to keep it as a separate git submodule. To simplify
modification of this script, we move it here.

If the linux64 mar-tools is not available, use any of the other
mar-tools that is available.

Asked by GeKo on IRC.

When checking our .mar and .exe files for signing errors we keep the
checked files around until the whole check is done. This essentially
leads to doubling the amount of disk space for them during that time,
which could make the difference between someone being able to check
them successfully or not.

There is actually no need, though, to keep all the binaries until the
whole signature check is done and we remove the checked bundle from now
on immediately after a particular check finished.

Update the tor-browser-bundle-testsuite.git commit, to add
android-aarch64 nightly builds.

At the same time, we update the tor-browser-bundle-testsuite.git URL to
use the repository that created with #30516.

When creating a new keyring with gpg >= 2.1, it will be created in the
keybox format, which is only compatible with gpg >= 2.1. This means that
the drop-expired-sub-keys script will create keyring files which are not
compatible with older versions of gpg.

To avoid this, we use the output of gpg --export as the keyring file,
which is in the old format.

The tools/keyring/drop-expired-sub-keys script can be used to drop all
expired and revoked sub-keys from a keyring.

We also add the script tools/keyring/list-all-keyrings which can be used
to list all the keys included in all the keyring files, to make it
easier to review if any key needs to be removed.

By default dma will send emails by connecting to the configured mail
server on port 25.

According to https://riseup.net/en/email/clients we should be connecting
to mail.riseup.net on port 587.

With #26843 we now require mercurial to be installed, so it should be
installed by the tbb-build ansible role.

Arthur said he doesn't need access to this machine anymore, so we remove
his user account from the ansible config (the account will be removed
from the machine manually).

Update testsuite_git_commit to remove tor browser alpha nightly builds.

Update testsuite_git_commit to enable android nightly builds.

Add the option `mar_compression` to update_responses_config.yml to
select the compression format used in the mar files.

Currently we are using bzip2 for the previous alpha, xz for the new
alpha, and bzip2 for both the previous and new stable.

Add the whitespace in "Tor Browser.app".

Use make_path instead of mkdir to create all needed parent directories.