CLI: require stdin.isatty before using cli.input

The cli.input method currently blindly calls either
raw_input or getpass both of which hang if stdin is
piped into the bin/omero command. A further fix here
would be to teach the input method itself how to check
stdin, but this require a more further review.

See
https://trello.com/c/mUAfr6kf/200-bin-omero-should-fail-if-not-logged-in-and-no-stdin

Former-commit-id: bc59894

src/omero/plugins/sessions.py

@@ -448,6 +448,9 @@ def login(self, args):
                 action = "Reconnected to"
 
         if not rv:
+
+            self._require_tty("cannot request password")
+
             tries = 3
             while True:
                 try:
@@ -883,6 +886,7 @@ def _get_server(self, store, name, port):
         defserver = store.last_host()
         if not port:
             port = str(omero.constants.GLACIER2PORT)
+        self._require_tty("cannot request server")
         rv = self.ctx.input("Server: [%s:%s]" % (defserver, port))
         if not rv:
             return defserver, name, port
@@ -892,12 +896,18 @@ def _get_server(self, store, name, port):
     def _get_username(self, defuser):
         if defuser is None:
             defuser = get_user("root")
+        self._require_tty("cannot request username")
         rv = self.ctx.input("Username: [%s]" % defuser)
         if not rv:
             return defuser
         else:
             return rv
 
+    def _require_tty(self, msg):
+        if sys.stdin.isatty():
+            return
+        self.ctx.die(564, "stdin is not a terminal: %s" % msg)
+
 
 try:
     register("sessions", SessionsControl, HELP)