Support host configuration for docker-daemon sources and destinations

This PR adds CLI support for overriding the default docker daemon host when using the
`docker-daemon` transport.

Fixes #244

Signed-off-by: Justin Lewis Salmon <justin.lewis.salmon@gmail.com>

completions/bash/skopeo

@@ -31,6 +31,8 @@ _skopeo_copy() {
     --dest-cert-dir
     --dest-ostree-tmp-dir
     --dest-tls-verify
+    --src-daemon-host
+    --dest-daemon-host
     "
 
     local boolean_options="