fixup! Bring back file-based OTA edify functions

(1) install.cpp is now used to build a host library as well,
    and glibc's xattr.h does not include the kernel header
    unlike its bionic counterpart, so manually include it.

(2) UpdaterRuntimeInterface is also implemented by
    SimulatorRuntime for which we would need to define the
    sehandle() function.
    Provide a default implementation which returns null.

Change-Id: If458678b87f871a9b3fd2269d9299ed9eb190c7f