[sonic-mgmt] Fix "fdb/test_fdb_mac_move.py" AttributeError failure (#…

…15704)

Test is relying on duthost method "get_crm_resources" method (parses
info from "crm show resources all" output)  to get "fdb_entry" crm
resource values. If output is empty for some reason then
"duthost.get_crm_resources().get("main_resources")" will be empty and thus
lead to "AttributeError: 'NoneType' object has no attribute 'get' during
get_crm_resources()" failure if we try to access "fdb_entry" key.

PR#11127 has introduced retry mechanism in case of empty output but condition is
incorrect ("len(duthost.get_crm_resources())") will never be 0. Correcting this
PR change to check for "main_resources" fixes the issue.

tests/fdb/utils.py

@@ -31,10 +31,12 @@ def IntToMac(intMac):
 def get_crm_resources(duthost, resource, status):
     retry_count = 5
     count = 0
-    while len(duthost.get_crm_resources()) == 0 and count < retry_count:
+    while len(duthost.get_crm_resources().get("main_resources")) == 0 and count < retry_count:
         logger.debug("CRM resources not fully populated, retry after 2 seconds: count: {}".format(count))
         time.sleep(2)
         count = count + 1
+    pytest_assert(resource in duthost.get_crm_resources().get("main_resources"),
+                  "{} not populated in CRM resources".format(resource))
     return duthost.get_crm_resources().get("main_resources").get(resource).get(status)