upgrade: Show fewer stacktraces.

The stacktraces here are seldom useful -- for the calls to
upgrade-stage-2, we know precisely what was run.  For the `run`
wrapper, the output contains the command that failed, which is
sufficient to identify where in the upgrade process it was.  Showing
more stacktrace below the actual error merely confuses users and
scrolls the real error off of the screen.

scripts/lib/upgrade-zulip-from-git

@@ -85,13 +85,18 @@ try:
 
     overwrite_symlink(deploy_path, os.path.join(DEPLOYMENTS_DIR, "next"))
 
-    subprocess.check_call(
-        [
-            os.path.join(deploy_path, "scripts", "lib", "upgrade-zulip-stage-2"),
-            deploy_path,
-            "--from-git",
-            *deploy_options,
-        ]
-    )
+    try:
+        subprocess.check_call(
+            [
+                os.path.join(deploy_path, "scripts", "lib", "upgrade-zulip-stage-2"),
+                deploy_path,
+                "--from-git",
+                *deploy_options,
+            ]
+        )
+    except subprocess.CalledProcessError:
+        # There's no use in showing a stacktrace here; it just hides
+        # the error from stage 2.
+        sys.exit(1)
 finally:
     release_deployment_lock()