Improve declaring python dependencies

package.xml

@@ -15,6 +15,9 @@
   <exec_depend>rospy</exec_depend>
   <exec_depend>rosbridge_library</exec_depend>
   <exec_depend>std_msgs</exec_depend>
+  <exec_depend>python-inject-pip</exec_depend>
+  <exec_depend>python-msgpack</exec_depend>
+  <exec_depend>python-paho-mqtt</exec_depend>
 
   <export>
   </export>

requirements.txt

 inject>=3.3.1
-nose>=1.3.7
-nose-ignore-docstring>=0.2
 paho-mqtt>=1.2
 msgpack-python>=0.4.8