pkg/idtools: use string-literals for easier grep'ing

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 1da079f211396ea6030a60ca37848d3c1f7dd99b)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/idtools/idtools_unix_test.go

@@ -459,14 +459,14 @@ func TestLookupUserAndGroup(t *testing.T) {
 func TestLookupUserAndGroupThatDoesNotExist(t *testing.T) {
 	fakeUser := "fakeuser"
 	_, err := LookupUser(fakeUser)
-	assert.Check(t, is.Error(err, "getent unable to find entry \""+fakeUser+"\" in passwd database"))
+	assert.Check(t, is.Error(err, `getent unable to find entry "fakeuser" in passwd database`))
 
 	_, err = LookupUID(-1)
 	assert.Check(t, is.ErrorContains(err, ""))
 
 	fakeGroup := "fakegroup"
 	_, err = LookupGroup(fakeGroup)
-	assert.Check(t, is.Error(err, "getent unable to find entry \""+fakeGroup+"\" in group database"))
+	assert.Check(t, is.Error(err, `getent unable to find entry "fakegroup" in group database`))
 
 	_, err = LookupGID(-1)
 	assert.Check(t, is.ErrorContains(err, ""))