test: Added --jobs option

Default to the number of CPU cores, which seems about optimal
on my laptop. Using one more saves me 2 seconds actually.

Better packing of workers improves speed significantly.

In 2 tests runs, I saw segfaulting workers despite my attempt
to work around that issue. So detect when a worker does, and re-run it.

Removed installSignalHandlers again, because I was seeing an
error "lost signal due to full pipe", which I guess was somehow caused
by using it.

Sponsored-by: Dartmouth College's Datalad project

Types/Test.hs

@@ -1,6 +1,6 @@
 {- git-annex test data types.
  -
- - Copyright 2011-2017 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2022 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -8,27 +8,16 @@
 module Types.Test where
 
 import Test.Tasty.Options
-import Data.Monoid
-import qualified Data.Semigroup as Sem
-import Prelude
 
+import Types.Concurrency
 import Types.Command
 
 data TestOptions = TestOptions
 	{ tastyOptionSet :: OptionSet
 	, keepFailuresOption :: Bool
 	, fakeSsh :: Bool
+	, concurrentJobs :: Maybe Concurrency
 	, internalData :: CmdParams
 	}
 
-instance Sem.Semigroup TestOptions where
-	a <> b = TestOptions
-		(tastyOptionSet a <> tastyOptionSet b)
-		(keepFailuresOption a || keepFailuresOption b)
-		(fakeSsh a || fakeSsh b)
-		(internalData a <> internalData b)
-
-instance Monoid TestOptions where
-	mempty = TestOptions mempty False False mempty
-
 type TestRunner = TestOptions -> IO ()