resources: Rename 'x86-ubuntu-img' -> 'x86-ubuntu-18.04-img'

As we may make disk images of different versions of Ubuntu, this
resource has been renamed. The older name has been deprecated and will
be removed. We deprecate to give us time to update references to it
elsewhere.

Change-Id: I8d2aaffc21b2892dc2aca47058e7d94d373b44c0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-resources/+/51170
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
diff --git a/resources.json b/resources.json
index f7e4cf1..9252b8e 100644
--- a/resources.json
+++ b/resources.json
@@ -47,6 +47,16 @@
         {
             "type" : "resource",
             "name" : "x86-ubuntu-img",
+            "documentation" : "An x86 disk image with Ubuntu 18.04. [This is deprecated. Please use 'x86-ubuntu-18.04-img'].",
+            "architecture" : "X86",
+            "is_zipped" : true,
+            "md5sum" : "90e363abf0ddf22eefa2c7c5c9391c49",
+            "url" : "{url_base}/images/x86/ubuntu-18-04/x86-ubuntu.img.gz",
+            "source" : "src/x86-ubuntu"
+        },
+        {
+            "type" : "resource",
+            "name" : "x86-ubuntu-18.04-img",
             "documentation" : "An x86 disk image with Ubuntu 18.04.",
             "architecture" : "X86",
             "is_zipped" : true,