pySim-shell: permit string with spaces for 'echo' command

before this patch:

pySIM-shell (00:MF)> echo foo bar baz
usage: echo [-h] string
echo: error: unrecognized arguments: bar baz

after this patch:

pySIM-shell (00:MF)> echo foo bar baz
foo bar baz

Change-Id: I1369bc3aa975865e3a8a574c132e469813a9f6b9
---
M pySim-shell.py
1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/pySim-shell.py b/pySim-shell.py
index d9c9f8c..306dd40 100755
--- a/pySim-shell.py
+++ b/pySim-shell.py
@@ -510,13 +510,13 @@
             first = False
 
     echo_parser = argparse.ArgumentParser()
-    echo_parser.add_argument('string', help="string to echo on the shell")
+    echo_parser.add_argument('string', help="string to echo on the shell", nargs='+')
 
     @cmd2.with_argparser(echo_parser)
     @cmd2.with_category(CUSTOM_CATEGORY)
     def do_echo(self, opts):
         """Echo (print) a string on the console"""
-        self.poutput(opts.string)
+        self.poutput(' '.join(opts.string))
 
     @cmd2.with_category(CUSTOM_CATEGORY)
     def do_version(self, opts):

