RFR: JDK-8189094: Change required boot jdk to JDK 9

[Martin Buchholz]

I tried to figure out how this patch actually works.  At first I thought we
were "shading" (renaming all the packages in the source files) but now I
think we're merely renaming the modules by appending ".interim" to the
names.  But that looks like cheating to me - we're not allowed to have
multiple modules containing the same packages, but are getting away with it
because the runtime happens to never look at the (unused) original jdk9
modules?