python: Set program name to the true name instead of 'python'.

As in commit e102bcf3cf (for Perl), any
Python program has the handle program name field set to 'python'.  Set
it to the true name (derived from sys.argv[0]).

generator/python.ml

@@ -671,6 +671,8 @@ logvols = g.lvs ()
 
 \"\"\"
 
+import os
+import sys
 import libguestfsmod
 
 ";
@@ -714,6 +716,10 @@ class GuestFS(object):
         self._o = libguestfsmod.create (flags)
         self._python_return_dict = python_return_dict
 
+        # If we don't do this, the program name is always set to 'python'.
+        program = os.path.basename (sys.argv[0])
+        libguestfsmod.set_program (self._o, program)
+
     def __del__ (self):
         if self._o:
             libguestfsmod.close (self._o)