[stateless] readonly-root support

[Bill Nottingham]

Initial readonly root support will be in tomorrow's initscripts-8.33-1.

How to use:

- Edit /etc/sysconfig/readonly-root. Set 'READONLY' to 'yes'.
- Add any exceptions that need to be writable that aren't in the
  stock /etc/rwtab to an /etc/rwtab.d file. (See below)

** NOTE: This does not currently work with SELinux. We're working on it. **
     
How it works:

- On boot, we mount a tmpfs (by default, at /var/lib/stateless/writable),
  and then parse /etc/rwtab and /etc/rwtab.d/* for things to put there.

  These files have the format:

<type>	<path>

  Types are as follows:
  
  empty: An empty path. Example:
  	'empty	/tmp'
  
  dirs: A directory tree that is copied, empty. Example:
  	'dirs	/var/run'

  files: A file or directory tree that is copied intact. Example:
  	'files	/etc/resolv.conf'

  A stock rwtab is shipped with common things that need mounted. We're
  currently investigating other things. If you come up with new ones,
  please file a bug.

Problems should be filed in bugzilla at https://bugzilla.redhat.com/, 
product Fedora Core, release devel, component initscripts.

Things we know need work:
- a simple 'prepare' script for a filesystem that is intended to
  be mounted read-only - it will update various caches (beagle,
  locate), clean out extraneous temporary files, and build the
  SELinux policy module.
- using local storage automatically for swap, etc.
- the rest of http://fedoraproject.org/wiki/StatelessLinux :)

Bill