The reason we are doing drop root is so that a network exposed
software component (i.e. glance) cannot be used to affect the
immutability of the container which it runs in. I have tried
several different approaches and this is the only approach which
puts glance in PID=1 while ensuring no files may be written by
the glance process in the container image except for the log files.
Change-Id: Ifd3c8c361b78d0e4791dade3afa6435290407c41
Partially-Implements: blueprint drop-root
6cf5928ff1