Move busy detection of SWRaid members into the new module (#756829)

Add active attribute to the cache of SWRaid members.  Move parsing of
/proc/mdstat to discover busy SWRaid members into the cache loading
code.  New parsing code is a little different because it is finding all
members of active arrays rather than determining if a specific member is
active.

Bug 756829 - SWRaid member detection enhancements