Update to improved system_properties API.

/// Gets the value of a system property on Android

#[cfg(target_os = "android")]

pub fn get(name: &str) -> Option<String> {

    rustutils::system_properties::read(name).ok()

    rustutils::system_properties::read(name).unwrap_or(None)

}

/// Fake getter for non-Android, which will always return nothing.