conf/*.xsl: move shared stuff to common.xsl

Not yet for xml2conf.xsl (e.g., new-line) as common.xsl would have to be
marked for installation along this one as it is used in deployment.

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
conf/corosync.rnc: votequorum(5) reference in the quorum section

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>