[c-c create] make post-create step optional (closes #2712041)
In this context the "post-create" step refers to the database's creation and
initialization. We want to be able to create a new instance but skip the
database creation (`db-create` and `db-init` commands) in automatic setup.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html