Allow microdroid_manager to create a /apex/* file

Microdroid_manager needs to pass APEX pubkeys to APEXd. Since the data
is too big for a system property, it creates a file
/apex/vm-payload-metadata so that APEXd reads/uses it.

Bug: 199371341
Test: MicrodroidHostTestCases
Change-Id: Iaf2b4fc08b36610032d9c339f787e5e34994448b
1 file changed