Added a test case for fast reboot from other vendor NOS to SONiC.

Details:
A new test case was added to fast reboot script.
This test case mimics a fast reboot from other vendor nos to SONiC, by flushing all DBs that
are part of the boot process, so the boot will be initiated with clean DBs as if it was booting from other nos.

tests/common/fixtures/advanced_reboot.py

@@ -117,7 +117,7 @@ def __extractTestParam(self):
         if self.rebootLimit is None:
             if self.kvmTest:
                 self.rebootLimit = 200 # Default reboot limit for kvm
-            elif 'warm-reboot' in self.rebootType:
+	    elif 'warm-reboot' in self.rebootType:
                 self.rebootLimit = 0
             else:
                 self.rebootLimit = 30 # Default reboot limit for physical devices

tests/platform_tests/test_advanced_reboot.py

@@ -55,8 +55,9 @@ def test_fast_reboot_from_other_vendor(duthosts,  rand_one_dut_hostname, request
     duthost = duthosts[rand_one_dut_hostname]
     advancedReboot = get_advanced_reboot(rebootType='fast-reboot', other_vendor_nos = True,\
     advanceboot_loganalyzer=advanceboot_loganalyzer)
-    preboot_oper = flush_dbs(duthost)
-    advancedReboot.runRebootTestcase(preboot_setup = preboot_oper)
+    # Before rebooting, we will flush all unnecessary databases, to mimic reboot from other vendor.
+    flush_dbs(duthost)
+    advancedReboot.runRebootTestcase()
 
 @pytest.mark.device_type('vs')
 def test_warm_reboot(request, get_advanced_reboot, verify_dut_health,
@@ -158,4 +159,5 @@ def flush_dbs(duthost):
                         6: 'State DB'
                }
     for db in db_dic.keys():
-        duthost.shell('redis-cli -n {} flushdb'.format(db))
+        duthost.shell('redis-cli -n {} flushdb'.format(db))
+