fix: get ssh username from ~/.ssh/config, if not specified in uri

[pnsafonov]

Fix allows to use

provider "libvirt" {
 uri ="qemu+ssh://mn0/system?no_verify=1&sshauth=privkey"
}

in addition to:

provider "libvirt" {
 uri = "qemu+ssh://p.safonov@mn0/system?no_verify=1&sshauth=privkey"
}

Then username is specified in ~/.ssh/config:

Host micronode0 mn0
    User p.safonov # read this string
    Port 22
    HostName 10.128.4.38
    IdentityFile /home/pavel/.ssh/server/pp/pp_mn0
    IdentitiesOnly yes

Summary by CodeRabbit

• Bug Fixes

  • Improved SSH connection reliability by ensuring user configuration overrides are applied consistently.

• Refactor

  • Streamlined internal SSH configuration handling for enhanced stability and maintainability.

[dmacvicar]

I'd like to deprecate the current ssh transport instead of adding support to more config options, in favour of the transport based on the native ssh command.

Is there a way you could help us testing those use cases will work in the new transport instead?