Use distro pip on Ubuntu

Running get-pip.py fails on Ubuntu when running twice, e.g. after a
unstack/stack cycle. Just use distro pip instead.

Closes-Bug: #1957048
Signed-off-by: Dr. Jens Harbott <harbott@osism.tech>
Change-Id: I87a8d53ed8860dd017a6c826dee6b6f4baef3c96
1 file changed