Add mapping for python-dev for Ubuntu Focal
Add mapping for python-dev for Ubuntu Focal

In Ubuntu Focal there is no package named 'python-dev'.
This patch maps this to 'python3-dev'.

Change-Id: I2ea41c36d13748dd5a375853b26aacfc63c1bd48
Signed-off-by: Andreas Florath <692e36d52fccd43fbbe98f18cd7ed640ecedf40e@telekom.de>
Closes-Bug: 1865328

openstack/tripleo-image-elements,openstack/tripleo-image-elements