rework system connection and farm storage

We now no longer write containers.conf, instead system connections and
farms are written to a new file called podman-connections.conf.

This is a major rework and I had to change a lot of things to get this
to compile again with my c/common changes.

It is a breaking change for users as connections/farms added before this
commit can now no longer be removed or modified directly. However because
the logic keeps reading from containers.conf the old connections can
still be used to connect to a remote host.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

vendor/github.com/containers/common/pkg/config/config_unix.go

@@ -0,0 +1,25 @@
+//go:build !windows
+
+package config
+
+import (
+	"os"
+	"path/filepath"
+
+	"github.com/containers/storage/pkg/unshare"
+)
+
+// userConfigPath returns the path to the users local config that is
+// not shared with other users. It uses $XDG_CONFIG_HOME/containers...
+// if set or $HOME/.config/containers... if not.
+func userConfigPath() (string, error) {
+	if configHome := os.Getenv("XDG_CONFIG_HOME"); configHome != "" {
+		return filepath.Join(configHome, _configPath), nil
+	}
+	home, err := unshare.HomeDir()
+	if err != nil {
+		return "", err
+	}
+
+	return filepath.Join(home, UserOverrideContainersConfig), nil
+}