getIndexBuildOpId is a util test function for index build jstests.

The test failed because we can have the createIndexes collection match the input collection collectionName in getIndexBuildOpId, with op.ns: [databaseName].$cmd. This means that we will say that we succeeded to complete the index build when we haven't in the collection [databaseName].collectionName in function waitForIndexBuildToStart (which depends on the result of getIndexBuildOpId)