44638: roachtest: continue running if test panics r=nvanbenschoten a=tbg

We didn't run most roachtests tonight because the sqlsmith roachtest
panicked in `.Generate()` (ironic I know).

Obviously a panicking test ought not be able to mess with roachtest
in that way. Translate the panic into a test failure and carry on.

Release note: None

Co-authored-by: Tobias Schottdorf <[email protected]>