separate paste-deploy configuration from parameters

PasteDeploy configuration contains class names which might change
between releases. Keeping it separate from user-configurable
parameters allows deployers to move paste-deploy ini file out of
configuration directory to a place where it can be safely overwritten
on updates e.g. under /usr/share/

DocImpact

Change-Id: I9292ca6226c8430b93565dedd45cc842742a23e2
Merge "separate paste-deploy configuration from parameters"