For now apk's path should be specified in the config. But in the future
it will be retrieved from apk package name. APK file's idsig is not
passed yet.
Bug: n/a
Test: MicrodroidHostTestCases
Change-Id: I6916c657b29b72a809a69f8be41c2398314e0178
Microdroid will use this special partition composed of signatures to
verify the payloads delivered from the host.
For now it only conveys the list of APEX signatures: size, public key,
root digest.
The signature partition can be a part of the payload composite disk
image.
The format of the signature partition is, as described in README.md,
composed of header and body. For now the header is simply the size of
the body(protobuf message).
Bug: 185069443
Test: n/a
Change-Id: I47c7eac195999bab15ee80d3ad053261f04df89c
Jooyung Han