esx_vi_generator: Simplify alignment function

Generate whitespace using the standard function ljust() that is
available in both Py3 [1] and Py2 [2].

1: https://docs.python.org/3/library/stdtypes.html?highlight=strip#str.ljust
2: https://docs.python.org/2.7/library/string.html#string.ljust

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Radostin Stoyanov <rstoyanov1@gmail.com>

src/esx/esx_vi_generator.py

@@ -49,10 +49,7 @@ separator = "/* " + ("* " * 37) + "*\n"
 
 
 def aligned(left, right, length=59):
-    while len(left) < length:
-        left += " "
-
-    return left + right
+    return left.ljust(length, ' ') + right