Allowed empty ssh password for remote launching

[5tan]

Bug in roslaunch doesn't allow to use empty ssh passwords.

E.g. If we try following machine definition:

<machine
  name="mmm"
  address="10.20.73.2"
  user="root"
  password=""
  timeout="10"
  env-loader="/path/to/remote-env.sh"
/>

Empty string is going to be replaced with None here:

ros_comm/tools/roslaunch/src/roslaunch/core.py

Line 350 in d39a5ec

self.password = password or None

(because empty strings are being treated as False in boolean operations).
Then, instead of authenticating using empty password, roslauch will attempt to use a key:

ros_comm/tools/roslaunch/src/roslaunch/remoteprocess.py

Line 189 in 7671747

if not password: #use SSH agent

After the change (this pull request) everything works as expected:

Case	Result
password="abc"	authentication using password
password=""	authentication using (empty) password
password attribute absent in machine definition	authentication using key

[dirk-thomas]

Thanks for the patch.