Fix the dockerfiles downloading Falco tar.gz package with ADD from URL

[leodido]

Describe the bug

When the FALCO_VERSION env variable contains a version string with a character like + the resulting URL to download the TAR.GZ package does not resolve correctly.

For example, this is happening here:

falco/docker/minimal/Dockerfile

Line 11 in 802b9f7

ADD https://s3.amazonaws.com/download.draios.com/stable/tgz/x86_64/falco-${FALCO_VERSION}-x86_64.tar.gz /

To solve this the URL needs to be url-encoded.

How to reproduce it

Try to build the docker/minimal image using FALCO_VERSION=0.20.0+d77080a.

Expected behavior

The ADD command to fetch the tar.gz package correctly from its URL.

Environment

• Falco version: 0.20.0

• System info:

• Cloud provider or hardware configuration:
• OS: Arch Linux

• Kernel: Linux l13o1 5.4.10-arch1-1 Digwatch compiler #1 SMP PREEMPT Thu, 09 Jan 2020 10:14:29 +0000 x86_64 GNU/Linux

• Installation method:

Additional context

The same applies when downloading the Falco packages with curl.

[leodido]

/assign

/milestone 0.21.0