[advanced-reboot] Improve error reporting in ansible log

[stepanblyschak]

Description of PR

Summary: [advanced-reboot] Improve error reporting in ansible log
Fixes # (issue)

Type of change

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

Approach

How did you do it?

Log error not only in ptf log file but also to ansible log.
Also fix a bug with threading even initialization and reachability watcher thread start order

How did you verify/test it?

From the ansible log there is only "Something went wrong message", now it is more verbose and outputs specific failure reason:
e.g.:

ok: [mts-sonic-dut-t0] => {
    "out.stdout_lines": [
        "WARNING: No route found for IPv6 destination :: (no default route?)",
        "advanced-reboot.ReloadTest ... FAIL",
        "",
        "======================================================================",
        "FAIL: advanced-reboot.ReloadTest",
        "----------------------------------------------------------------------",
        "Traceback (most recent call last):",
        "  File \"ptftests/advanced-reboot.py\", line 720, in runTest",
        "    self.assertTrue(is_good, errors)",
        "AssertionError: ",
        "",
        "Something went wrong. Please check output below:",
        "",
        "FAILED:dut:Control plane didn't come up within warm up timeout",
        "FAILED:dut:DUT is not ready for test",
        "",
        "",
        "----------------------------------------------------------------------",
        "Ran 1 test in 240.056s",
        "",
        "FAILED (failures=1)"
    ]
}

ok: [mts-sonic-dut-t0] => {
    "out.stdout_lines": [
        "WARNING: No route found for IPv6 destination :: (no default route?)",
        "advanced-reboot.ReloadTest ... FAIL",
        "",
        "======================================================================",
        "FAIL: advanced-reboot.ReloadTest",
        "----------------------------------------------------------------------",
        "Traceback (most recent call last):",
        "  File \"ptftests/advanced-reboot.py\", line 720, in runTest",
        "    self.assertTrue(is_good, errors)",
        "AssertionError: ",
        "",
        "Something went wrong. Please check output below:",
        "",
        "FAILED:dut:DUT hasn't shutdown in 300 seconds",
        "",
        "",
        "----------------------------------------------------------------------",
        "Ran 1 test in 382.915s",
        "",
        "FAILED (failures=1)"
    ]

Any platform specific information?

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

Documentation