`tools/ubuntu-setup/all.sh` stops while installing `python-pip` on Ubuntu 20.04

## Environment details:

* Linux VM running on VMWare ESXi
* Ubuntu 20.04.2 LTS focal

## Steps to reproduce the issue:
I followed `tools/setup-ubuntu/README.md`.

1. Clone this repository
2. Run `tools/ubuntu-setup/all.sh` with no arguments

## Provide the expected results and outputs:
I expected the installation completes successfully.

## Provide the actual results and outputs:
It failed to install package `python-pip` with the following error message.

```
+ echo '*** installing python dependences'
*** installing python dependences
+ /bin/bash ./pip.sh
+ sudo apt-get install -y python-pip
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package python-pip is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
python3-pip

E: Package 'python-pip' has no installation candidate
```

## Additional information you deem important:
* All other installations/initializations were successful except for `python-pip`.
* So I installed `python3-pip` manually as the above message suggests, and skipped `pip.sh` in the script by commenting out.
* Then it works.