cdaa749ba0
Add missing wait for Slg4 introduced in f8299bc ("MINOR: log: "drop"
support for log-profile steps"), and missing barrier increase due to
the use of barrier sync, which could have resulted in the regtest
being timing-sentive and thus less-reliable.
Also, the "error" check in Slg4 wasn't even considered because it is
emitted by frontend 4, not frontend 2..
No backport needed unless f8299bc is.