Prevent dropping or altering of reserved predicates.

[martinmr]

There is already logic to prevent certain internal predicates (ACL and
type preds) from being dropped by a DropAll request. This change adds
similar logic to prevent DropAttr and Schema requests from modifying or
dropping reserved predicates.

---

This change is 

[manishrjain]

Reviewed 1 of 2 files at r1, 1 of 1 files at r2.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @golangcibot and @martinmr)

---

edgraph/server.go, line 287 at r2 (raw file):

	// Reserved predicates cannot be dropped.
	if _, ok := x.InitialPreds[op.DropAttr]; len(op.DropAttr) > 0 && ok {

Let's keep the flow of code the same. We don't need to do this upfront. Move this to under op.DropAll.

---

edgraph/server.go, line 295 at r2 (raw file):

	updates, schemaErr := schema.Parse(op.Schema)
	if schemaErr == nil {
		for _, update := range updates {

Move this to under the previous schema.Parse section.

[martinmr]

Reviewable status: 1 of 2 files reviewed, 3 unresolved discussions (waiting on @golangcibot and @manishrjain)

---

edgraph/server.go, line 286 at r1 (raw file):

Previously, golangcibot (Bot from GolangCI) wrote…

File is not goimports-ed (from goimports)

Done.

---

edgraph/server.go, line 287 at r2 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

Let's keep the flow of code the same. We don't need to do this upfront. Move this to under op.DropAll.

Done.

---

edgraph/server.go, line 295 at r2 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

Move this to under the previous schema.Parse section.

Done.

Addressed comments. Ready for another review.

[martinmr]

I didn't realized that the test was broken after I addressed the comments in the previous review. I have fixed that and this is ready for another round of review.

[codexnull]

Reviewed 2 of 2 files at r3.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @golangcibot and @manishrjain)

[manishrjain]

Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @golangcibot and @manishrjain)