fix(test): fix guest_kernel metric in boottime tests

The search-and-replace for excluding the no-acpi kernels from the
performance tests was a bit overzealous and also renames the
`guest_kernel` metric.

Fixes: 2360fcc
Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

tests/integration_tests/performance/test_boottime.py

@@ -181,7 +181,7 @@ def test_boottime(
         {
             **DIMENSIONS,
             "performance_test": "test_boottime",
-            "guest_kernel_acpi": guest_kernel_acpi.name,
+            "guest_kernel": guest_kernel_acpi.name,
             "vcpus": str(vcpu_count),
             "mem_size_mib": str(mem_size_mib),
         }