[Libguestfs] [PATCH nbdkit 0/9] Create libnbdkit.so

This creates libnbdkit.so as discussed in the following thread: https://www.redhat.com/archives/libguestfs/2020-March/thread.html#00203 test-delay-shutdown.sh fails for unclear reasons. This series starts by reverting "tests: Don't strand hung nbdkit processes" which is because several other tests fail randomly unless I revert this patch. I didn't investigate this yet so it could be caused by this patch series. libtool on Linux doesn't appear to care about -undefined/-no-undefined. See comments in commit messages. The patch is kind of ugly TBH. Personally I don't have a problem with plugins having undefined references that are later resolved to the main binary, but I understand that Windows is broken in this regard. Rich.