slap/standalone: Add comment about slapos binary

Standalone uses the path of a slapos binary passed as a parameter to
run slapos commands with supervisord or as subprocesses, instead of
recreating an entry point script into the slapos version currently
running standalone. Normally the slapos binary provided is actually
the same slapos. One reason to do it this way is that in test nodes,
standalone is run with pygolang's gpython which doesn't support
running buildout (buildout tries to reexec with -S).

slapos/slap/standalone.py

@@ -443,6 +443,10 @@ class StandaloneSlapOS(object):
     self._ipv6_range_prefixlen = None
     self._partitions_have_ipv6_range = False
 
+    # NOTE: Using Standalone's own slapos (slapos.cli.entry) instead
+    # is not that easy because in test nodes standalone is often run
+    # with gpython (pygolang), and gpython currently doesn't support
+    # buildout
     self._slapos_bin = slapos_bin
 
     self._slapos_commands = {