Use pip to install ipython, not apt-get

I am very unsure that it will install ipython for all required python versions

tests/install.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 pip install .
-pip install psutil
+pip install psutil ipython
 if python -c 'import sys; sys.exit(1 * (sys.version_info[0] != 2))' ; then
 	# Python 2
 	if python -c 'import platform, sys; sys.exit(1 - (platform.python_implementation() == "CPython"))' ; then
@@ -12,7 +12,7 @@ if python -c 'import sys; sys.exit(1 * (sys.version_info[0] != 2))' ; then
 		pip install unittest2 argparse
 	fi
 fi
-sudo apt-get install -qq screen zsh tcsh mksh busybox ipython
+sudo apt-get install -qq screen zsh tcsh mksh busybox
 # Travis has too outdated fish. It cannot be used for tests.
 # sudo apt-get install fish
 true