Use more robust regex matching in rollback resumable index build fixture

For synchronization reasons, the rawMongoProgramOutput with assert.soon is used to wait for the log line

5113600 [conn] "Hanging in getLog"

Currently we are only matching the log id, which can be coincidentally in other parts of the log like

"electionTime":\{"$date":{"$numberLong":"6995113600343867393"}}