crash-manager: don't store in zip archive files referred by symlinks

crash-manager: don't store in zip archive files referred by symlinks

minicoredump (will be introduced in next commit) has an option to save
/proc/<pid>/ files in report. As /proc/<pid>/fd/* contains symlinks, the
created archive will contain the contents of these fds. This is
undesirable as files might be quite big and contain private (sensitive)
data.

This commit adds -y option to zip, which will allow storing symlinks to
actual files instead of their contents (as it was available originally
under /proc/<pid>/)"

Change-Id: I0a7c9211eab1acd39da7db3930e967ddab5eceef