instead of using hardcoded disk, let ssdutil to determine the default…

… disk device

tests/platform_tests/cli/test_show_platform.py

@@ -313,15 +313,13 @@ def test_show_platform_ssdhealth(duthosts, enum_supervisor_dut_hostname):
     @summary: Verify output of `show platform ssdhealth`
     """
     duthost = duthosts[enum_supervisor_dut_hostname]
-    cmd = "cat /sys/block/sda/queue/rotational"
-    ssdcheck_output_lines = duthost.command(cmd)["stdout_lines"]
-    if '0' not in ssdcheck_output_lines:
-       pytest.skip("Disk type is not SSD")
-
     cmd = " ".join([CMD_SHOW_PLATFORM, "ssdhealth"])
 
     logging.info("Verifying output of '{}' on ''{}'...".format(cmd, duthost.hostname))
     ssdhealth_output_lines = duthost.command(cmd)["stdout_lines"]
+    if 'not SSD' in ssdcheck_output_lines:
+       pytest.skip("Disk type is not SSD")
+
     ssdhealth_dict = util.parse_colon_speparated_lines(ssdhealth_output_lines)
     expected_fields = set(["Device Model", "Health", "Temperature"])
     actual_fields = set(ssdhealth_dict.keys())