upload_manifest.py opens a port to the world, and always the same port

[nyh]

We've seen Jenkins runs fail, e.g., http://jenkins.cloudius-systems.com:8080/job/osv-build-nightly/1666/console, because port 10000 was not available during the build. Presumably because a previous build hung and kept it open, or some other program on the system used the same port number.

upload_manifest.py uses port 10000 on the host to communicate with the cpiod inside the guest to install files.

Firstly, we should trivially modify it to pick the host port randomly instead of always using "10000" (note that one of the occurances in "10000" in that code - the guest port number - should remain unchanged).

Secondly, we should modify the --forward line to only open this port inside the host - not to the entire world. This is also very easy - instead of "--forward tcp::1234-:10000'" do "--forward tcp:127.0.0.1:1234-:10000'

There's a similar issue for imgedit.py: see issue #709.