install.sh: remove obsolete packages and try to maintain the python version being used by the host

Author: ramonfontes

.travis.yml

@@ -18,7 +18,7 @@ before_install:
 
 install:
 - pip install pexpect || pip3 install pexpect
-- sudo util/install.sh -Wlnfvw6
+- sudo util/install.sh -Wlnfv6
 
 script:
 - sudo mn --wifi --test pingall
@@ -27,4 +27,4 @@ script:
 notifications:
   email:
     on_success: never
-# More details: https://docs.travis-ci.com/user/notifications#Configuring-email-notifications
+# More details: https://docs.travis-ci.com/user/notifications#Configuring-email-notifications