Make Persistatant grub vars respect existing ones

We were basically overwriting the file if it existed which is bad.
Now it will read the file if it exists and ingest the existing ones,
then in will override witht he given vars if they match, warn the user
and then store the full processed vars.

This means it will never overwrite any vars again

Signed-off-by: Itxaka <itxaka@kairos.io>

pkg/utils/utils_test.go

@@ -804,9 +804,9 @@ var _ = Describe("Utils", Label("utils"), func() {
 				defer os.Remove(temp.Name())
 				Expect(utils.SetPersistentVariables(
 					temp.Name(), map[string]string{"key1": "value1", "key2": "value2"},
-					config.Fs,
+					config,
 				)).To(BeNil())
-				readVars, err := utils.ReadPersistentVariables(temp.Name(), config.Fs)
+				readVars, err := utils.ReadPersistentVariables(temp.Name(), config)
 				Expect(err).To(BeNil())
 				Expect(readVars["key1"]).To(Equal("value1"))
 				Expect(readVars["key2"]).To(Equal("value2"))
@@ -814,7 +814,7 @@ var _ = Describe("Utils", Label("utils"), func() {
 			It("Fails setting variables", func() {
 				e := utils.SetPersistentVariables(
 					"badfilenopath", map[string]string{"key1": "value1"},
-					config.Fs,
+					config,
 				)
 				Expect(e).NotTo(BeNil())
 			})