Add darwin support for remote-client

Add the ability to cross-compile podman remote for OSX.

Also, add image exists and tag to remote-client.

Signed-off-by: baude <bbaude@redhat.com>

libpod/runtime_volume_unsupported.go

@@ -0,0 +1,19 @@
+// +build !linux
+
+package libpod
+
+import (
+	"context"
+)
+
+func (r *Runtime) removeVolume(ctx context.Context, v *Volume, force, prune bool) error {
+	return ErrNotImplemented
+}
+
+func (r *Runtime) newVolume(ctx context.Context, options ...VolumeCreateOption) (*Volume, error) {
+	return nil, ErrNotImplemented
+}
+
+func (r *Runtime) NewVolume(ctx context.Context, options ...VolumeCreateOption) (*Volume, error) {
+	return nil, ErrNotImplemented
+}