hst/container: optional runtime and tmpdir sharing

Sharing and persisting these directories do not always make sense. Make it optional here.

Closes #16.

Signed-off-by: Ophestra <cat@gensokyo.uk>

hst/hst_test.go

@@ -244,7 +244,9 @@ func TestTemplate(t *testing.T) {
 		"tty": true,
 		"multiarch": true,
 		"map_real_uid": true,
-		"device": true
+		"device": true,
+		"share_runtime": true,
+		"share_tmpdir": true
 	}
 }`