tests/kms_chamelium: Wait for chamelium being reachable after a suspend

Getting network back after waking up from suspend takes some time.
If it's not quick enough, it may cause any following chamelium_rpc
to fail.

This includes the chamelium port reset in exit handler:

	igt_chamelium-CRITICAL: Test assertion failure function chamelium_rpc,
				file ../lib/igt_chamelium.c:349:
	igt_chamelium-CRITICAL: Failed assertion: !chamelium->env.fault_occurred
	igt_chamelium-CRITICAL: Last errno: 113, No route to host
	igt_chamelium-CRITICAL: Chamelium RPC call failed: libcurl failed to execute
				the HTTP POST transaction, explaining:
				Failed to connect to 192.168.1.224 port 9992: No route to host

	Stack trace:
	  #0 ../lib/igt_core.c:1674 __igt_fail_assert()
	  #1 [chamelium_rpc+0x1ea]
	  #2 ../lib/igt_chamelium.c:2274 chamelium_reset()
	  #3 ../lib/igt_chamelium.c:2361 chamelium_deinit()
	  #4 ../lib/igt_core.c:2124 call_exit_handlers()

So let's wait for Chamelium to be reachable after each suspend_autoresume.

v2: Bump the network timeout to 20s,
    the slowest observed bring-up was 17s. (Petri)
    Do not DECREF if we get NULL from __chmelium_rpc(). (Simon & CI)

Cc: Simon Ser <simon.ser@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109380


Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Reviewed-by: Simon Ser <simon.ser@intel.com>