Upgrading non taskcluster linux CI machines

Process for upgrading build machines from Trusty to Xenial:

sudo apt update
sudo apt dist-upgrade
do-release-upgrade

After restarting the machine, to resolve incompatible packages:

add-apt-repository ppa:ubuntu-toolchain-r/test
wget http://security.ubuntu.com/ubuntu/pool/main/g/gcc-5/libstdc++6_5.4.0-6ubuntu1~16.04.10_amd64.deb
dpkg -i libstdc++6_5.4.0-6ubuntu1~16.04.10_amd64.deb
rm libstdc++6_5.4.0-6ubuntu1~16.04.10_amd64.deb

# For cross builders:
wget http://security.ubuntu.com/ubuntu/pool/main/g/gcc-5/libstdc++6_5.4.0-6ubuntu1~16.04.10_i386.deb
dpkg -i libstdc++6_5.4.0-6ubuntu1~16.04.10_i386.deb
rm libstdc++6_5.4.0-6ubuntu1~16.04.10_i386.deb
apt install gcc-5-base=5.4.0-6ubuntu1~16.04.10 gcc-5-base:i386=5.4.0-6ubuntu1~16.04.10 cpp-5=5.4.0-6ubuntu1~16.04.10 gcc-5-base=5.4.0-6ubuntu1~16.04.10 libstdc++-5-dev=5.4.0-6ubuntu1~16.04.10 libgcc-5-dev=5.4.0-6ubuntu1~16.04.10 g++-5=5.4.0-6ubuntu1~16.04.10 gcc-5=5.4.0-6ubuntu1~16.04.10 libasan2=5.4.0-6ubuntu1~16.04.10 libmpx0=5.4.0-6ubuntu1~16.04.10

# For non-cross builders:
apt install gcc-5-base=5.4.0-6ubuntu1~16.04.10 cpp-5=5.4.0-6ubuntu1~16.04.10 g++-5=5.4.0-6ubuntu1~16.04.10 gcc-5=5.4.0-6ubuntu1~16.04.10 libstdc++-5-dev=5.4.0-6ubuntu1~16.04.10 libgcc-5-dev=5.4.0-6ubuntu1~16.04.10 libasan2=5.4.0-6ubuntu1~16.04.10 libmpx0=5.4.0-6ubuntu1~16.04.10 libstdc++-5-dev=5.4.0-6ubuntu1~16.04.10

apt autoremove

service salt-minion start