A resource which generates random strings for passwords

Orchestrated services often need passwords and secrets to be propagated to multiple servers and set in configuration files or admin tools.

Currently the only practical way of doing this is to define template parameters for passwords and specify the password value on stack create. This can become a burden for complex templates with many services. For example these tripleo examples ask the user to generate 13 random passwords to pass to stack-create:
http://docs.openstack.org/developer/tripleo-incubator/devtest.html

This blueprint suggests creating a resource type OS::Heat::RandomString which randomly generates a string that can be accessed via an attribute. Properties can be set to specify what kind of string to generate, but defaults would aim to generate a string which is appropriate for service and user passwords that heat templates typically configure.

The resource's string will be stored in resource data and will be persisted by heat for the lifecycle of the stack. A future modification could be to store the string on a key server like Barbican.