Fix installation script for containerd on armhf

[welteki]

Description

Fix installation script for containerd on armhf, by downloading from alexellis/containerd-arm as per previous script version - a88997e

The script also requires an updated version of arkade to support the cni system app on armhf:
https://github.com/alexellis/arkade/releases/tag/0.8.34

Motivation and Context

Fixes #295
Closes #296

How Has This Been Tested?

Tested installation script with updated arkade version on pi3 running 32-bit Raspberry Pi OS lite.

Verified status with

sudo journalctl -u faasd --lines 100 -f

Deployed and invoked figlet function from store

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Commits:

• I've read the CONTRIBUTION guide
• My commit message has a body and describe how this was tested and why it is required.
• I have signed-off my commits with git commit -s for the Developer Certificate of Origin (DCO)

Code:

• My code follows the code style of this project.
• I have added tests to cover my changes.

Docs:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.