Add "mountdefaultencrypted" command to vdc.

It's being used by the emulator.

Test: vdc --wait cryptfs mountdefaultencrypted
Bug: 65795120
Change-Id: I8a5d622e4fa1ef93bb8e22f2665c882b1a152b3d

vdc.cpp

@@ -96,6 +96,8 @@ int main(int argc, char **argv) {
         int encryptionFlags = android::os::IVold::ENCRYPTION_FLAG_IN_PLACE
                 | android::os::IVold::ENCRYPTION_FLAG_NO_UI;
         exit(vold->fdeEnable(passwordType, "", encryptionFlags).isOk() ? 0 : ENOTTY);
+    } else if (arg1 == "cryptfs" && arg2 == "mountdefaultencrypted") {
+        exit(vold->mountDefaultEncrypted().isOk() ? 0 : ENOTTY);
     } else if (arg1 == "volume" && arg2 == "shutdown") {
         exit(vold->shutdown().isOk() ? 0 : ENOTTY);
     } else {