[vs] Skip MACsec clean up if /sbin/ip is not accessible (sonic-net#750)

Some build containers for sonic-buildimage may not have ip command, and for non MACsec test's this is not required to be present.

vslib/src/MACsecManager.cpp

@@ -5,6 +5,8 @@
 #include <swss/logger.h>
 #include <swss/exec.h>
 
+#include <unistd.h>
+
 #include <regex>
 #include <cstring>
 #include <system_error>
@@ -833,6 +835,12 @@ void MACsecManager::cleanup_macsec_device() const
 {
     SWSS_LOG_ENTER();
 
+    if (access("/sbin/ip", F_OK) == -1)
+    {
+        SWSS_LOG_WARN("file /sbin/ip not accessible, skipping");
+        return;
+    }
+
     std::string macsecInfos;
 
     if (!exec("/sbin/ip macsec show", macsecInfos))