Fix sh script

[aaron7]

• Fix TMPFILE generation
• Use lowercase for distribution name
• Show downloading message as there is a small delay

[aaron7]

There is another problem - here we have get.weave.works hardcoded, however dev uses get.dev.weave.works

Should we allow a flag to override this or perhaps have the service template install.sh to include the correct hostname?

cc @dlespiau

[dlespiau]

The more user friendly way would be to serve an install.sh script with the correct hostname already in.