RecoverySystem: Verify the package compatibility.

This CL extends the existing API RecoverySystem.verifyPackage() to
verify the compatibility entry in an OTA package. It returns true
directly if such an entry doesn't exist. Otherwise it reads and passes
the contents to VintfObject to perform the verification.

This CL also adds a new system API
RecoverySystem.verifyPackageCompatibility() to verify a given
compatibility zip file. It extracts all the entries and passes them to
VintfObject.verify() to verify the package compatibility. This API is
for streaming A/B OTAs only, where we don't download the full package
but only needed entries.

Bug: 36592877
Bug: 36596980
Test: RecoverySystem.verifyPackage() returns the same result for
      packages w/o a compatibility entry.
Change-Id: I038be672868a91820c045d1da100e8e33b23d442