pool.pp: add new define ceph::pool

Added new ceph::pool to manage pools. Currently these actions are supported:
- create a new pool (via $create_pool, defaults to false)
- delete an existing pool from the cluster (via $delete_pool, defaults to
  false) -> BE VERY CAREFULLY WITH THIS PARAMETER!
- increase pg_num of a pool (via $increase_pg_num, defaults to false)
- increase pgp_num of a pool (via $increase_pgp_num, defaults to false)

fixed typo in 'describe' of ceph_key_spec.rb (s/wen/when/).

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
README.rst: add hint on how to run the rspec tests

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>