Fixed compile warning

FlattenedCompositeModuleOptionsMetadata.java:152: warning:
[rawtypes] found raw type: EnumerablePropertySource
	EnumerablePropertySource propertySource = mo.asPropertySource();
	^
missing type arguments for generic class EnumerablePropertySource<T>
where T is a type-variable
XD-1686: Pluralize admins group node

- Since we support multiple admin servers and all of them participate in leadership election,
it might be good pluralizing the leadership group path's node name

/xd/admin -> /xd/admins