chore: udpate sample_latency to use FCMetricsMonitor

FCMetricsMonitor class relies on `microvm` having a valid
`kernel_file` to set guest kernel dimensions.
sample_latency test restores microvm from snapshot so it
didn't need to have a guest kernel passed while building
microvm object.
Passing guest kernel shouldn't affect the restore test
but it will help FCMetricsMonitor to get the right guest
kernel version so, update `sample_latency` to pass guest
kernel while building the microvm.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Author: Sudan Landge

tests/integration_tests/performance/test_snapshot_ab.py

@@ -77,12 +77,15 @@ def configure_vm(
 
         return vm
 
-    def sample_latency(self, microvm_factory, snapshot) -> List[float]:
+    def sample_latency(
+        self, microvm_factory, snapshot, guest_kernel_linux_4_14
+    ) -> List[float]:
         """Collects latency samples for the microvm configuration specified by this instance"""
         values = []
 
         for _ in range(ITERATIONS):
             microvm = microvm_factory.build(
+                kernel=guest_kernel_linux_4_14,
                 monitor_memory=False,
             )
             microvm.spawn()
@@ -162,6 +165,7 @@ def test_restore_latency(
     samples = test_setup.sample_latency(
         microvm_factory,
         snapshot,
+        guest_kernel_linux_4_14,
     )
 
     for sample in samples: