Allow feature to run last

[fwilhe]

What would you like to be added:

Allow to specify a feature type for 'run this feature last'. This option may only at max be used once in all features in a build.

Why is this needed:

While working on the STIG PR for GL, it was occuring to me that as a user of the builder, I don't think I can influence in which order the features are run. So for example, if I have 3 features that have all a exec.config script, in which order will they be run?

For STIG, the feature needs to run last because it will apply compliance settings. No other feature should be able to override what the STIG feature is doing (for example in the sshd config).

[fwilhe]

For example, there could be a feature type compliance. STIG may be one example of that, but other compliance features may exist. compliance features can't be combined, they exclude each other by definition.