allow joins to work properly with k3sExtraArgs

[billimek]

Description

Using the --k3s-extra-args command-line argument failed during a join operation.

Motivation and Context

Fixes #30

How Has This Been Tested?

Reproduced the issue,

➜ k3sup join --ip 10.2.0.31 --server-ip 10.2.0.30 --user ubuntu --k3s-extra-args '--docker'
Server IP: 10.2.0.30
ssh -i /Users/jeff/.ssh/id_rsa [email protected]
ssh: sudo cat /var/lib/rancher/k3s/server/node-token

<redacted>
ssh: curl -sfL https://get.k3s.io/ | K3S_URL="https://10.2.0.30:6443" K3S_TOKEN="<redacted>" sh - --docker
sh: 0: Can't open --docker

After correcting the issue,

1. validated that the normal behavior (without specifying the --k3s-extra-args argument) still works as expected:

➜ bin/k3sup-darwin join --ip 10.2.0.31 --server-ip 10.2.0.30 --user ubuntu                            
Server IP: 10.2.0.30
ssh -i /Users/jeff/.ssh/id_rsa [email protected]
ssh: sudo cat /var/lib/rancher/k3s/server/node-token

<redacted>
ssh: curl -sfL https://get.k3s.io/ | K3S_URL='https://10.2.0.30:6443' K3S_TOKEN='<redacted>' sh -s - 
[INFO]  Finding latest release
...

2. validated that the --k3s-extra-args behavior now works:

➜ bin/k3sup-darwin join --ip 10.2.0.31 --server-ip 10.2.0.30 --user ubuntu --k3s-extra-args '--docker'
Server IP: 10.2.0.30
ssh -i /Users/jeff/.ssh/id_rsa [email protected]
ssh: sudo cat /var/lib/rancher/k3s/server/node-token

<redacted>
ssh: curl -sfL https://get.k3s.io/ | K3S_URL='https://10.2.0.30:6443' K3S_TOKEN='<redacted>' sh -s - --docker
[INFO]  Finding latest release
...

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:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.

[alexellis]

Bill, thank you for working on this.

Shall we test the method that generates this string now that it's become more complex than when I started?

https://blog.alexellis.io/golang-writing-unit-tests/

[alexellis]

Approved

[alexellis]

@billimek it would be much appreciated if you could write some unit tests for the generation of the strings in various scenarios.

See my link on how to get started and reach out if you'd like help.