[tests] if no ptf host in testbed.csv get it from inventory

[stepanblyschak]

Signed-off-by: Stepan Blyschak stepanb@mellanox.com

Description of PR

Summary:
Fixes # (issue)

02:08:09         "ansible_adhoc = <function init_host_mgr at 0x7f19ecd395f0>", 
02:08:09         "testbed = {'comment': 'Mellanox MTBC testbed', 'dut': 'mtbc-sonic-03-2700', 'group-name': 'vm-t1', 'ptf_image_name': 'docker-ptf-mlnx', ...}", 
02:08:09         "", 
02:08:09         "    @pytest.fixture(scope='module')", 
02:08:09         "    def ptfadapter(ansible_adhoc, testbed):", 
02:08:09         "        \"\"\"return ptf test adapter object.", 
02:08:09         "        The fixture is module scope, because usually there is not need to", 
02:08:09         "        restart PTF nn agent and reinitialize data plane thread on every", 
02:08:09         "        test class or test function/method. Session scope should also be Ok,", 
02:08:09         "        however if something goes really wrong in one test module it is safer", 
02:08:09         "        to restart PTF before proceeding running other test modules", 
02:08:09         "        \"\"\"", 
02:08:09         "    ", 
02:08:09         ">       ptfhost = AnsibleHost(ansible_adhoc, testbed['ptf'])", 
02:08:09         "E       KeyError: 'ptf'", 

Type of change

• Bug fix
• [] Testbed and Framework(new/improvement)
• [] Test case(new/improvement)

Approach

How did you do it?

Get ptf_host from inventory

How did you verify/test it?

Run test with pdb and access ptf_host when no ptf in testbed.csv

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation

[liat-grozovik]

please add more information in the commit message itself.
i am missing bug description as for sure you are fixing some issue found

[liat-grozovik]

@stepanblyschak should this fix be merged to 201811? if so, need to set label.