Support empty jacoco-report-classes.jar

If EMMA_INSTRUMENT is turned on but no APKs were built the rule to
collect jacoco-report-classes.jar would error with missing directories
and an empty zip file.  Switch to soong_zip, which doesn't error
on empty zip files, and hide the errors if $(TARGET_COMMON_OUT_ROOT)
or $(HOST_COMMON_OUT_ROOT) don't exist.

Test: m EMMA_INSTRUMENT=true TARGET_BUILD_APPS=Camera2
Change-Id: I09e30e37dc38f32f55b3f91bfc4d12c9e753083f