skip test_memory_exhaustion on Celestica-E1031 (#8007)

What is the motivation for this PR?
1. Skip testcase test_memory_exhaustion on Celestica-E1031 platform. `tail /dev/zero` cannot always trigger an OOM kernel panic on this platform.
2. Keep the keys in tests_mark_conditions_platform_tests.yaml in alphabetical order.

How did you do it?
Use conditional mark to skip the testcase on Celestica-E1031 platform.

How did you verify/test it?
Verified on Celestica-E1031 testbed.

Signed-off-by: Zhijian Li <zhijianli@microsoft.com>

Author: lizhijianrd

tests/common/plugins/conditional_mark/tests_mark_conditions_platform_tests.yaml

@@ -761,6 +761,15 @@ platform_tests/mellanox/test_reboot_cause.py:
     conditions:
       - "platform in ['x86_64-mlnx_msn2010-r0', 'x86_64-mlnx_msn2700-r0', 'x86_64-mlnx_msn2100-r0', 'x86_64-mlnx_msn2410-r0', 'x86_64-nvidia_sn2201-r0']"
 
+#######################################
+####  test_memory_exhaustion.py   #####
+#######################################
+platform_tests/test_memory_exhaustion.py:
+  skip:
+    reason: "Unsupported release or platforms"
+    conditions:
+      - "(is_multi_asic==True and release in ['201911']) or (hwsku in ['Celestica-E1031-T48S4'])"
+
 #######################################
 #####    test_platform_info.py    #####
 #######################################