This patch permits symlinks in the docker build. Normally docker
does not permit symlinked files in the build context sent to the
docker server. To work around this problem, a secure directory
is created in /tmp and the container contents are copied to that
directory. Any symlinks are turned into their non-symlinked
equivalents.
Change-Id: I38cd5aeed4c73b90449354a0979fc6ddf7891ccb
Implements-blueprint: linked-build
1078eddf11