bot: Use Mercurial with Python 3 (mozilla#365)

Fixes mozilla#332

Author: marco-c

bot/ci/bootstrap.sh

@@ -4,12 +4,9 @@ MERCURIAL_VERSION="5.2"
 VERSION_CONTROL_TOOLS_REV="102106f53cb2"
 
 apt-get update
-apt-get install --no-install-recommends -y gcc curl bzip2 python2-minimal python-bz2file python-dev
+apt-get install --no-install-recommends -y gcc curl bzip2 python-dev
 
-# Setup mercurial from its own website, without install pip2 which has a lot of dependencies
-curl -L https://www.mercurial-scm.org/release/mercurial-$MERCURIAL_VERSION.tar.gz | tar -C /opt -xvz
-cd /opt/mercurial-$MERCURIAL_VERSION
-python2 setup.py install
+pip install --disable-pip-version-check --quiet --no-cache-dir mercurial==$MERCURIAL_VERSION
 
 # Setup grcov
 curl -L https://github.com/mozilla/grcov/releases/download/$GRCOV_VERSION/grcov-linux-x86_64.tar.bz2 | tar -C /usr/bin -xjv
@@ -20,7 +17,7 @@ hg clone -r $VERSION_CONTROL_TOOLS_REV https://hg.mozilla.org/hgcustom/version-c
 ln -s /src/bot/ci/hgrc $HOME/.hgrc
 
 # Cleanup
-apt-get purge -y gcc curl python-dev
+apt-get purge -y gcc curl bzip2 python-dev
 apt-get autoremove -y
 rm -rf /var/lib/apt/lists/*
 rm -rf /src/version-control-tools/.hg /src/version-control-tools/ansible /src/version-control-tools/docs /src/version-control-tools/testing