Skip the recent tests if the DUT version is 201911 or older. (#2797)

Skip the recent tests if the image is 201911 or older. These tests are added for the recent telemetry features which is available in 202012.

What is the motivation for this PR?
Prevent false test failures for 201911 images.

How did you do it?
Using pytest.skip conditionally.

Co-authored-by: Murat Acikgoz <muacikgo@microsoft.com>

tests/telemetry/test_telemetry.py

@@ -4,6 +4,7 @@
 import re
 import pytest
 
+from pkg_resources import parse_version
 from tests.common.helpers.assertions import pytest_assert
 from tests.common.utilities import wait_until, wait_tcp_connection
 
@@ -103,6 +104,12 @@ def setup_streaming_telemetry(duthosts, rand_one_dut_hostname, localhost,  ptfho
     file_exists = ptfhost.stat(path="/gnxi/gnmi_cli_py/py_gnmicli.py")
     pytest_assert(file_exists["stat"]["exists"] is True)
 
+def skip_201911_and_older(duthost):
+    """ Skip the current test if the DUT version is 201911 or older.
+    """
+    if parse_version(duthost.kernel_version) <= parse_version('4.9.0'):
+        pytest.skip("Test not supported for 201911 images. Skipping the test")
+
 # Test functions
 def test_config_db_parameters(duthosts, rand_one_dut_hostname):
     """Verifies required telemetry parameters from config_db.
@@ -166,6 +173,7 @@ def test_osbuild_version(duthosts, rand_one_dut_hostname, ptfhost, localhost):
     """ Test osbuild/version query.
     """
     duthost = duthosts[rand_one_dut_hostname]
+    skip_201911_and_older(duthost)
     cmd = generate_client_cli(duthost=duthost, method=METHOD_GET, target="OTHERS", xpath="osversion/build")
     show_gnmi_out = ptfhost.shell(cmd)['stdout']
     result = str(show_gnmi_out)
@@ -181,6 +189,7 @@ def test_sysuptime(duthosts, rand_one_dut_hostname, ptfhost, setup_streaming_tel
     """
     logger.info("start test the dataset 'system uptime'")
     duthost = duthosts[rand_one_dut_hostname]
+    skip_201911_and_older(duthost)
     dut_ip = duthost.mgmt_ip
     cmd = 'python /gnxi/gnmi_cli_py/py_gnmicli.py -g -t {0} -p {1} -m get -x proc/uptime -xt OTHERS \
            -o "ndastreamingservertest"'.format(dut_ip, TELEMETRY_PORT)
@@ -223,6 +232,7 @@ def test_virtualdb_table_streaming(duthosts, rand_one_dut_hostname, ptfhost, loc
     logger.info('start virtual db sample streaming testing')
 
     duthost = duthosts[rand_one_dut_hostname]
+    skip_201911_and_older(duthost)
     cmd = generate_client_cli(duthost=duthost, method=METHOD_SUBSCRIBE, update_count = 3)
     show_gnmi_out = ptfhost.shell(cmd)['stdout']
     result = str(show_gnmi_out)