Fix issues found by "go vet"

Issues were:

 # github.com/rfjakob/gocryptfs/contrib/findholes/holes
 contrib/findholes/holes/holes.go:136:2: unreachable code
 # github.com/rfjakob/gocryptfs/tests/root_test_test
 tests/root_test/root_test.go:139:2: unreachable code

Also make sure we actually run "go vet" against the whole
codebase.

contrib/findholes/holes/holes.go

@@ -121,7 +121,7 @@ func Find(fd int) (segments []Segment, err error) {
 		if err == syscall.ENXIO {
 			segments = append(segments,
 				Segment{totalSize, SegmentEOF})
-			return segments, nil
+			break
 		}
 		if err != nil {
 			return nil, err
@@ -136,7 +136,7 @@ func Find(fd int) (segments []Segment, err error) {
 	return segments, nil
 }
 
-// Verify the gives `segments` using a full bytewise file scan
+// Verify `segments` using a full bytewise file scan
 func Verify(fd int, segments []Segment) (err error) {
 	last := segments[len(segments)-1]
 	if last.Type != SegmentEOF {

test.bash

@@ -50,7 +50,7 @@ if ! go tool | grep vet > /dev/null ; then
 elif [[ -d vendor ]] ; then
 	echo "vendor directory exists, skipping 'go tool vet'"
 else
-	go vet "$@" .
+	go vet "$@" ./...
 fi
 
 if command -v shellcheck > /dev/null ; then

tests/root_test/root_test.go

@@ -136,7 +136,6 @@ func writeTillFull(t *testing.T, path string) (int, syscall.Errno) {
 		}
 		sz += n
 	}
-	return sz, 0
 }
 
 // TestDiskFull needs root permissions because it creates a loop disk