use this horrible complex bit of shell to make sure that curl doesn't hand the poor user a broken docker client

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
mention the tgz - other people might like to know

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
OSX mktemp is different - hopfully this will now work on HP/UX >:}

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #4764 from SvenDowideit/use-docker-tgz

Use docker tgz file to download on OSX