Don't copy files if /var/log is a symlink

When doing the initial move of logfiles to /var/log to the pool a number
of precautions are taken to ensure that the existing logfiles are preserved.

After /var/log is symlinked to ${poolname}/syslog/log things like
cat /var/log/messages >> ${poolname}/syslog/log/messages do
something fairly harmful.

http://www.cs.uni.edu/~wallingf/teaching/cs3540/sessions/session11/python-tail-recursion.png
(cherry picked from commit 9458895379b77d62598eea367c78b4f8fe6e6268)