Install python-redis from pip

Following the leads of  I47b7e787771683c2fc4404e586f11c1a19aac15c and as
an attempt to fix a bug blocking Zaqar's gate, this patch installs
python-redis from pypi instead of using the distro package.

Change-Id: Idfef2fe1b41b44c4cba6b6948b621bc44e77659b

files/debs/zaqar-server

@@ -1,5 +1,4 @@
 python-pymongo
 mongodb-server
 pkg-config
-redis-server # NOPRIME
-python-redis # NOPRIME
+redis-server # NOPRIME

lib/zaqar

@@ -147,13 +147,13 @@ function configure_zaqar {
 function configure_redis {
     if is_ubuntu; then
         install_package redis-server
+        pip_install redis
     elif is_fedora; then
         install_package redis
+        pip_install redis
     else
         exit_distro_not_supported "redis installation"
     fi
-
-    install_package python-redis
 }
 
 function configure_mongodb {