Use database_ prefix for database parameters

A prefix is required to avoid any confusion about
the purpose of those parameters.

puppet-nova uses database_ for those parameters. It makes sense
to use the same in puppet-ironic.

This change breaks backward compatibility.

Change-Id: Id78f5c41a7d0ab0e9fe2430d1f8b9a2cc6a66e05
Attempt to apply common rspec style

Various fixes:
- Indentation, spaces, etc.
- Hash.merge! can accept multiple parameters
- Curly braces style

Change-Id: I18fab44bfd58b239d3bacd79b66d32cfa49bf0dc
Ensure database backend package is installed

Install database backend package according to database connection.

Change-Id: I927b80dc88f3120d6b4265c7aaa94d706780f50c
Merge "Use database_ prefix for database parameters"
Merge "Attempt to apply common rspec style"
Merge "Ensure database backend package is installed"