Fix etcd driver requirement

Etcd driver is included in common requirement project.
We do not need to explicitly install it in scripts.

Change-Id: I749ea3ae46d1f8e058770b6b9ec145536de0e698

devstack/etcd_driver

@@ -91,7 +91,7 @@ function nb_db_driver_install_server {
 }
 
 function nb_db_driver_install_client {
-    sudo pip install python-etcd
+    :
 }
 
 function nb_db_driver_status_server

requirements.txt

@@ -4,6 +4,7 @@
 
 pbr>=1.6 # Apache-2.0
 Babel>=2.3.4 # BSD
+python-etcd>=0.4.3 # MIT License
 kazoo>=2.2 # Apache-2.0
 ovs>=2.6.0 # Apache-2.0
 pyzmq>=14.3.1 # LGPL+BSD

tools/tox_install.sh

@@ -50,5 +50,4 @@ else
 fi
 
 $install_cmd -U $*
-pip install python-etcd
 exit $?