Fix a few bugs after initial testing.

- Read out of the regular config directly into temporary config.
- Replace </> with ++ in constructing the config name.
- Abort the CVMFS transaction.
Initially working version.
This is a rather large commit!

- New option (clone-only) that doesn't start a console.
- Automatically abort the CVMFS transaction on failure.
- Fix a bug in reading the LXC config file (failed on blank lines).
- Allow multiple values per key in the config (cgroups uses this).
- Sort the written config file output (LXC depends on this).
- When cleaning the capsule, make sure that the directories exist
  before trying to delete them.