container: use /proc/self/exe directly

This is a more reliable form of pathname to self and also cheaper than os.Executable.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/lockedfile/internal/filelock/filelock_test.go

@@ -14,7 +14,7 @@ import (
 	"testing"
 	"time"
 
-	"hakurei.app/container"
+	"hakurei.app/container/fhs"
 	"hakurei.app/internal/lockedfile/internal/filelock"
 	"hakurei.app/internal/lockedfile/internal/testexec"
 )
@@ -197,7 +197,7 @@ func TestLockNotDroppedByExecCommand(t *testing.T) {
 	// Some kinds of file locks are dropped when a duplicated or forked file
 	// descriptor is unlocked. Double-check that the approach used by os/exec does
 	// not accidentally drop locks.
-	cmd := testexec.CommandContext(t, t.Context(), container.MustExecutable(nil), "-test.run=^$")
+	cmd := testexec.CommandContext(t, t.Context(), fhs.ProcSelfExe, "-test.run=^$")
 	if err := cmd.Run(); err != nil {
 		t.Fatalf("exec failed: %v", err)
 	}

internal/lockedfile/lockedfile_test.go

@@ -15,7 +15,7 @@ import (
 	"testing"
 	"time"
 
-	"hakurei.app/container"
+	"hakurei.app/container/fhs"
 	"hakurei.app/internal/lockedfile"
 	"hakurei.app/internal/lockedfile/internal/testexec"
 )
@@ -215,7 +215,7 @@ func TestSpuriousEDEADLK(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	cmd := testexec.CommandContext(t, t.Context(), container.MustExecutable(nil), "-test.run=^"+t.Name()+"$")
+	cmd := testexec.CommandContext(t, t.Context(), fhs.ProcSelfExe, "-test.run=^"+t.Name()+"$")
 	cmd.Env = append(os.Environ(), fmt.Sprintf("%s=%s", dirVar, dir))
 
 	qDone := make(chan struct{})