Replace duplicate content with include

The section section_dashbard-install.xml contains a complete
copy of common/section_dashboard-configure.xml. Let's include
instead of duplicate.

Change-Id: I327766073717f4363aa2900dd9e94a564196a7cc
Closes-Bug: #1222006
Xen introduction content is no longer "common".

The Xen introduction file is no longer common content, it is only
referenced from the configuration reference guide.

Change-Id: Ia02da3050a29d1cee34323dcfc62a56abe2e70fa
Merge "Xen introduction content is no longer "common"."
Merge "Replace duplicate content with include"