bitbake: fetch2.URI: Set username/password should not change the other

When setting the username after already having set the password, the password
was unexpectedly reset. This change fixes this issue and introduces unit tests
to make sure it doesn't happen again.

(Bitbake rev: 25faef3a047f9c7564089463d7c96f6910b640cb)

Signed-off-by: Olof Johansson <olof.johansson@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/__init__.py

@@ -321,9 +321,10 @@ class URI(object):
 
     @username.setter
     def username(self, username):
+        password = self.password
         self.userinfo = username
-        if self.password:
-            self.userinfo += ":%s" % self.password
+        if password:
+            self.userinfo += ":%s" % password
 
     @property
     def password(self):