[Distributed] Set stdin to devnull before closing it (JuliaLang/julia#44881)

* [Distributed] Set stdin to devnull before closing it

Distributed closes and destroys stdin, but some tests attempted to
explicitly use it, leading to test problems. We previously interpreted
this as passing devnull, but this is better to be explicit.

* Revert "Testsystem: for now, move the REPL tests to node 1 (JuliaLang/julia#44880)"

This reverts commit 7401e92a930ab51ff74e67a27152df5c2acd459b.

Author: vtjnash

src/cluster.jl

@@ -232,7 +232,10 @@ start_worker(cookie::AbstractString=readline(stdin); kwargs...) = start_worker(s
 function start_worker(out::IO, cookie::AbstractString=readline(stdin); close_stdin::Bool=true, stderr_to_stdout::Bool=true)
     init_multi()
 
-    close_stdin && close(stdin) # workers will not use it
+    if close_stdin # workers will not use it
+        redirect_stdin(devnull)
+        close(stdin)
+    end
     stderr_to_stdout && redirect_stderr(stdout)
 
     init_worker(cookie)

test/distributed_exec.jl

@@ -1616,7 +1616,11 @@ cluster_cookie("")
 for close_stdin in (true, false), stderr_to_stdout in (true, false)
     local npids = addprocs_with_testenv(RetainStdioTester(close_stdin,stderr_to_stdout))
     @test remotecall_fetch(myid, npids[1]) == npids[1]
-    @test close_stdin != remotecall_fetch(()->isopen(stdin), npids[1])
+    if close_stdin
+        @test remotecall_fetch(()->stdin === devnull && !isreadable(stdin), npids[1])
+    else
+        @test remotecall_fetch(()->stdin !== devnull && isopen(stdin) && isreadable(stdin), npids[1])
+    end
     @test stderr_to_stdout == remotecall_fetch(()->(stderr === stdout), npids[1])
     rmprocs(npids)
 end