Use file glob for zipping classes*.dex files

Using a directory to zip the output of d8 and r8 was causing the
empty classes.dex.jar file in the output directory to get
zipped in.  Use a file glob instead so that it only picks up the
classes*.dex files even if classes.dex.jar already exists.

Test: m checkbuild
Change-Id: I1f3c1cbc23439fc52756aad027ab8cac10213d1d