Change python-devel to python-dev in Ubuntu CLI instructions
Change python-devel to python-dev in Ubuntu CLI instructions

This commit changes python-devel to python-dev for the Ubuntu section
of the CLI installation guide.

Change-Id: If591b0002d4e13bb8e3d0e987aca30ce5adef779
Closes-bug: 1424106

Akasurde/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,potsmaster/openstack-manuals,gongysh2004/openstack-manual,AlekhyaMallina-Vedams/openstack-manuals,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,potsmaster/openstack-manuals,saeki-masaki/openstack-manuals,gongysh2004/openstack-manual,kairoaraujo/openstack-manuals,openstack/openstack-manuals,kairoaraujo/openstack-manuals,openstack/openstack-manuals,Akasurde/openstack-manuals,openstack/openstack-manuals