configs,tests: Update refs to deprecated 'x86-ubuntu-img'

This resource has been deprecated in favor of 'x86-ubuntu-18.04-img'. In
practise, these are the same resource (i.e., the same disk image), but
we deprecate 'x86-ubuntu-img' as 'x86-ubuntu-18.04-img' is more explicit
on what the disk image contains. Going forward we may want different
disk image resources with different Ubuntu versions, and we want it to
be clear what the user is retrieving.

Change-Id: I06b08e6b65cf431067ffda35ebd10d419068d073
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54583
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/configs/example/gem5_library/x86-ubuntu-run-with-kvm.py b/configs/example/gem5_library/x86-ubuntu-run-with-kvm.py
index fa84960..1aea258 100644
--- a/configs/example/gem5_library/x86-ubuntu-run-with-kvm.py
+++ b/configs/example/gem5_library/x86-ubuntu-run-with-kvm.py
@@ -121,7 +121,7 @@
     kernel=Resource("x86-linux-kernel-5.4.49"),
     # The x86 ubuntu image will be automatically downloaded to the if not
     # already present.
-    disk_image=Resource("x86-ubuntu-img"),
+    disk_image=Resource("x86-ubuntu-18.04-img"),
     readfile_contents=command,
 )
 
diff --git a/configs/example/gem5_library/x86-ubuntu-run.py b/configs/example/gem5_library/x86-ubuntu-run.py
index c6f6f83..2aee8c7 100644
--- a/configs/example/gem5_library/x86-ubuntu-run.py
+++ b/configs/example/gem5_library/x86-ubuntu-run.py
@@ -58,7 +58,7 @@
 # downloaded.
 board.set_kernel_disk_workload(
     kernel=Resource("x86-linux-kernel-5.4.49"),
-    disk_image=Resource("x86-ubuntu-img"),
+    disk_image=Resource("x86-ubuntu-18.04-img"),
 )
 
 simulator = Simulator(board=board)
diff --git a/tests/gem5/configs/boot_kvm_fork_run.py b/tests/gem5/configs/boot_kvm_fork_run.py
index 2cd180a..662ef23 100644
--- a/tests/gem5/configs/boot_kvm_fork_run.py
+++ b/tests/gem5/configs/boot_kvm_fork_run.py
@@ -203,7 +203,7 @@
         resource_directory=args.resource_directory,
     ),
     disk_image=Resource(
-        "x86-ubuntu-img",
+        "x86-ubuntu-18.04-img",
         resource_directory=args.resource_directory,
     ),
     readfile_contents=dedent(
diff --git a/tests/gem5/configs/boot_kvm_switch_exit.py b/tests/gem5/configs/boot_kvm_switch_exit.py
index 9f5f7ee..5cfee40 100644
--- a/tests/gem5/configs/boot_kvm_switch_exit.py
+++ b/tests/gem5/configs/boot_kvm_switch_exit.py
@@ -188,7 +188,7 @@
         resource_directory=args.resource_directory,
     ),
     disk_image=Resource(
-        "x86-ubuntu-img",
+        "x86-ubuntu-18.04-img",
         resource_directory=args.resource_directory,
     ),
     # The first exit signals to switch processors.
diff --git a/tests/gem5/configs/x86_boot_exit_run.py b/tests/gem5/configs/x86_boot_exit_run.py
index 5c8b025..93c9028 100644
--- a/tests/gem5/configs/x86_boot_exit_run.py
+++ b/tests/gem5/configs/x86_boot_exit_run.py
@@ -207,7 +207,7 @@
         resource_directory=args.resource_directory,
     ),
     disk_image=Resource(
-        "x86-ubuntu-img",
+        "x86-ubuntu-18.04-img",
         resource_directory=args.resource_directory,
     ),
     kernel_args=kernal_args,