Add a generic utility to check any binary availability

In order to run, some test programs depend on the availability
of binaries in locations that are part of PATH. So, we add a
generic utility to simplify this.
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>

tests/python/utils.py

 from pyroute2 import NSPopen
 from distutils.spawn import find_executable
 
+def has_executable(name):
+    path = find_executable(name)
+    if path is None:
+        raise Exception(name + ": command not found")
+    return path
+
 class NSPopenWithCheck(NSPopen):
     """
     A wrapper for NSPopen that additionally checks if the program
@@ -11,8 +17,5 @@ class NSPopenWithCheck(NSPopen):
 
     def __init__(self, nsname, *argv, **kwarg):
         name = list(argv)[0][0]
-        path = find_executable(name)
-        if path is None:
-            raise Exception(name + ": command not found")
-        else:
+        has_executable(name)
         super(NSPopenWithCheck, self).__init__(nsname, *argv, **kwarg)