Dump server logs when corrupt fuzzer reports crash (#12612)

Recently we found some signal crashes, but unable to reproduce them.
It is a good idea to dump the server logs when a failure happens.

tests/integration/corrupt-dump-fuzzer.tcl

@@ -169,6 +169,11 @@ foreach sanitize_dump {no yes} {
                         incr stat_terminated_by_signal $by_signal
 
                         if {$by_signal != 0 || $sanitize_dump == yes} {
+                            if {$::dump_logs} {
+                                set srv [get_srv 0]
+                                dump_server_log $srv
+                            }
+
                             puts "Server crashed (by signal: $by_signal), with payload: $printable_dump"
                             set print_commands true
                         }

tests/test_helper.tcl

@@ -197,6 +197,12 @@ proc srv {args} {
     dict get $srv $property
 }
 
+# Take an index to get a srv.
+proc get_srv {level} {
+    set srv [lindex $::servers end+$level]
+    return $srv
+}
+
 # Provide easy access to the client for the inner server. It's possible to
 # prepend the argument list with a negative level to access clients for
 # servers running in outer blocks.