lxc remote add --protocol=simplestreams doesn't test connectivity until the remote is actually used

[simondeziel]

Steps to reproduce:

Confirm no connectivity to cloud-images.ubuntu.com:1234:

$ nc -zv cloud-images.ubuntu.com 1234
nc: connect to cloud-images.ubuntu.com (2620:2d:4000:1::1a) port 1234 (tcp) failed: Connection refused
nc: connect to cloud-images.ubuntu.com (2620:2d:4000:1::17) port 1234 (tcp) failed: Connection refused
nc: connect to cloud-images.ubuntu.com (185.125.190.37) port 1234 (tcp) failed: Connection refused
nc: connect to cloud-images.ubuntu.com (185.125.190.40) port 1234 (tcp) failed: Connection refused

Add that as a remote:

$ lxc remote add ubuntu1 https://cloud-images.ubuntu.com:1234/buildd/releases --protocol=simplestreams
$ echo $?
0

Test the remote:

$ lxc image list ubuntu1:
Error: Failed parsing stream: Get "https://cloud-images.ubuntu.com:1234/buildd/releases/streams/v1/index.json": Unable to connect to: cloud-images.ubuntu.com:1234 ([dial tcp [2620:2d:4000:1::1a]:1234: connect: connection refused dial tcp [2620:2d:4000:1::17]:1234: connect: connection refused dial tcp 185.125.190.37:1234: connect: connection refused dial tcp 185.125.190.40:1234: connect: connection refused])

[tomponline]

@simondeziel want to have a go at this one?

[simondeziel]

I can certainly take a crack at it but that won't be anytime soon.

[tomponline]

@gabrielmougard your PR broke adding simplestreams remotes so I am reverting this in #12446 for now.

Please can you try again, thanks.