tools (common/async_process): remove useless encoding + use full path for command:

- arguments don't need to be encoded anymore, `spawnProcess` handles str directly now
- use full path even for first argument: even if first argument should be only executable
  name, it appears that using full path only in `command` is not enough (seen with Python
  where system installation is used instead of the VirtualEnv one when full path is not
  used as first argument).
(grafted from 25cbaf04772855cd8aead18771465a4f00f5fa03)

sat/tools/common/async_process.py

@@ -114,8 +114,7 @@ class CommandProtocol(protocol.ProcessProtocol):
         if stdin is not None:
             stdin = stdin.encode('utf-8')
         verbose = kwargs.pop('verbose', False)
-        args = [a.encode('utf-8') for a in args]
-        kwargs = {k:v.encode('utf-8') for k,v in list(kwargs.items())}
+        args = list(args)
         d = defer.Deferred()
         prot = cls(d, stdin=stdin)
         if verbose:
@@ -131,7 +130,7 @@ class CommandProtocol(protocol.ProcessProtocol):
                 prot.name = name
         else:
             command = cls.command
-        cmd_args = [os.path.basename(command)] + args
+        cmd_args = [command] + args
         reactor.spawnProcess(prot,
                              command,
                              cmd_args,