[sonic-cfggen]: Fix syslog_server output (#9616)

Why I did it
'SYSLOG_SERVER': {'': {}, '10.0.10.5': {}, '10.0.10.6': {}},
Config db schema generated by minigraph can’t pass yang validation, server address can't be empty.

How I did it
Update test minigraph to remove wrong configuration.

How to verify it
Build sonic-config-engine.
Run command 'sonic-cfggen -m xxx.xml --print-data', and SYSLOG_SERVERS table.

Signed-off-by: Gang Lv ganglv@microsoft.com

src/sonic-config-engine/tests/sample-voq-graph.xml

@@ -109,7 +109,7 @@
     <a:DeviceProperty>
      <a:Name>SyslogResources</a:Name>
      <a:Value>
-      10.0.10.5;10.0.10.6;
+      10.0.10.5;10.0.10.6
      </a:Value>
     </a:DeviceProperty>
     <a:DeviceProperty>

src/sonic-config-engine/tests/simple-sample-graph-case.xml

@@ -446,7 +446,7 @@
     <a:DeviceProperty>
      <a:Name>SyslogResources</a:Name>
      <a:Value>
-      10.0.10.5;10.0.10.6;
+      10.0.10.5;10.0.10.6
      </a:Value>
     </a:DeviceProperty>
     <a:DeviceProperty>

src/sonic-config-engine/tests/simple-sample-graph-metadata.xml

@@ -245,7 +245,7 @@
     <a:DeviceProperty>
      <a:Name>SyslogResources</a:Name>
      <a:Value>
-      10.0.10.5;10.0.10.6;
+      10.0.10.5;10.0.10.6
      </a:Value>
     </a:DeviceProperty>
     <a:DeviceProperty>