Bootloader fails when its embedded key doesn't match with vbmeta's
signing key.
Note that VM itself doesn't shut down even when boot fails for now.
It should shut down the VM just like pvmfw does.
Bug: 218934597
Test: atest MicrodroidHostTestCases
Change-Id: I8bfef33d3aafe72f672c035fe796d8636bc95e1c
Jooyung Han