More robust book building for api-site

Build all manuals if check-build and --api-site is given since
dependency generation needs to be enhanced to handle XML and WADL files.

Change-Id: I8b5deeeac4a8b468036b503a2cde7d3ff3d9f60e

os_doc_tools/doctest.py

@@ -764,6 +764,11 @@ def build_affected_books(rootdir, book_exceptions,
     This will throw an exception if a book fails to build
     """
 
+    # Dependency generation in api projects does not work currently,
+    # thus build all books
+    if is_api_site:
+        force = True
+
     books = find_affected_books(rootdir, book_exceptions,
                                 verbose, force)