Makefile: bump e2e timeout to 90m

Test time was bumped in 4.8 from 75m to 90m via:
openshift#2474

Test has been failing often in 4.7 and will be a little longer
consistently as the exponential backoff has been removed in favor
of 5 min retries (which is faster in slower cases but a little
slower in faster cases).

(cherry picked from commit 654bd00)

Makefile

@@ -109,4 +109,4 @@ Dockerfile.rhel7: Dockerfile Makefile
 
 # This was copied from https://github.com/openshift/cluster-image-registry-operator
 test-e2e:
-	go test -failfast -timeout 75m -v$${WHAT:+ -run="$$WHAT"} ./test/e2e/
+	go test -failfast -timeout 90m -v$${WHAT:+ -run="$$WHAT"} ./test/e2e/