Provide way to correlate backgrounded index operation in currentOP() with index name

Currently, the index name is the key used to identify an index for the following:

• getIndexSpecs()
• getIndexes()
• db.system.indexes.find()

However, when backgrounding an index creation, the index name is not provided in currentOP() leaving no way to correlate a background index operation to the actual index. Another option could be to put the opid as reported in currentOP() in db.system.indexes.find() and subsequently report it in getIndexSpecs() and getIndexes().