doc: pass graphviz options in conf.py

easier to maintain the options of sphinx extensions in a single place.

Signed-off-by: Kefu Chai <kchai@redhat.com>

admin/build-doc

@@ -127,7 +127,6 @@ for target in $sphinx_targets; do
     case $target in
         html)
             builder=dirhtml
-            extra_opt="-D graphviz_output_format=svg"
             ;;
         man)
             extra_opt="-t man"

doc/conf.py

@@ -114,6 +114,9 @@ breathe_doxygen_config_options = {
 edit_on_github_project = 'ceph/ceph'
 edit_on_github_branch = 'master'
 
+# graphviz options
+graphviz_output_format = 'svg'
+
 def generate_state_diagram(input_paths, output_path):
     sys.path.append(os.path.join(top_level, 'doc', 'scripts'))
     from gen_state_diagram import do_filter, StateMachineRenderer