[Indexeddb] Changed attribute name from multientry to multiEntry

According to the deprecated standard, IndexedDB's Index object should
have attribute named "multientry". The latest standard says that
this attribute should be named "multiEntry" (e is uppercase).

BUG=XWALK-2203
Well, in these tests 'multientry' attribute isn't checked, it is only defined during execution of createIndex() method and it is not checked later, so these tests shouldn't fail because of wrong attribute.