Increase the readability of the configuration file

* document undocumented parameters
* group similiar parameters
* rename parameter 'stack_pass' to 'stack_password'
* use 'secretsecret' as default value for secrets ('secretsecret' is
  used in the OpenStack manuals as default value)
* add missing dots at the end of sentences
* use 79 chars per line

Change-Id: Ibc667c2375fe39443574e2c424033dd13479cba9