signzip: Prepare metadata file future support
signzip: Prepare metadata file future support

 * This new file is checked by AOSP recovery,
    however it is not required for the time being

Change-Id: I7d5815449316723debd956fa8e2b080f4aa0afb1
Signed-off-by: Adrian DC <01fb3892f39957945220431e7409156544d2f041@gmail.com>

AdrianDC/android_development_shell_tools,AdrianDC/android_development_shell_tools