ci: Use Packer to manage CI images

[mvines]

Currently we hand build our CI images on GCP (see ci/README.md). Instead let's use Packer to build the images from source and at the same time ideally make them portable between the different cloud providers

[mvines]

Manual steps to move the buildkite-agent home directory that should be done automatically by Packer:

1. Edit /etc/passwd to adjust the buildkite-agent home to /home/buildkite-agent
2. sudo mv /var/lib/buildkite-agent /home/
3. sudo ln -s /home/buildkite-agent /var/lib/buildkite-agent
4. Edit /etc/buildkite-agent/buildkite-agent.cfg and set build-path="/home/buildkite-agent/builds"

[mvines]

Packer should add these two lines to /lib/systemd/system/buildkite-agent.service in the [Service] section:

LimitNOFILE=65536

[pgarg66]

Added following lines to /etc/sysctl.conf
net.core.rmem_max=1610612736
net.core.rmem_default=1610612736

And, reload sysctl by
sudo sysctl -p

[pgarg66]

Added following lines to /etc/sysctl.conf
net.core.wmem_max=1610612736
net.core.wmem_default=1610612736

And, reload sysctl by
sudo sysctl -p

[pgarg66]

Added 64GB swap space to the machine.
` sudo fallocate -l 64G /swapfile

sudo chmod 600 /swapfile

sudo mkswap /swapfile

sudo swapon /swapfile

sudo swapon --show`

Add following line to /etc/fstab
/swapfile none swap sw 0 0

Change the swappiness to 10

• sudo sysctl vm.swappiness=10
• add vm.swappiness=10 to /etc/sysctl.conf

Reference: https://www.digitalocean.com/community/tutorials/how-to-add-swap-space-on-ubuntu-16-04

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[stale]

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