Support for pip3

[neillturner]

Most of distros nowadays use pip3, but omnibus and require_pip uses pip to try to install ansible...

[juju4]

also needed for centos/rhel8

https://travis-ci.org/juju4/ansible-harden-mailserver/jobs/600016390#L4136

-----> Installing Ansible Omnibus

       downloading https://raw.githubusercontent.com/neillturner/omnibus-ansible/master/ansible_install.sh

         to file /tmp/ansible_install.sh
[...]
      Complete!

CentOS-8 - AppStream                            2.8 kB/s | 4.3 kB     00:01    

CentOS-8 - Base                                 1.1 kB/s | 3.9 kB     00:03    

CentOS-8 - Extras                               841  B/s | 1.5 kB     00:01    

Extra Packages for Enterprise Linux 8 - x86_64  813 kB/s | 2.3 MB     00:02    

       Metadata cache created.

       Last metadata expiration check: 0:00:02 ago on Sat 19 Oct 2019 11:30:12 AM UTC.

       No match for argument: python-pip

       No match for argument: PyYAML

       No match for argument: python-jinja2

       No match for argument: python-httplib2

       No match for argument: python-keyczar

       No match for argument: python-paramiko

       Package git-2.18.1-3.el8.x86_64 is already installed.

       Error: Unable to find a match
[...]
       Last metadata expiration check: 0:00:04 ago on Sat 19 Oct 2019 11:30:12 AM UTC.

       No match for argument: python-devel

       No match for argument: MySQL-python

       Package libffi-devel-3.1-18.el8.x86_64 is already installed.

       Package openssl-devel-1:1.1.1-8.el8.x86_64 is already installed.

       Error: Unable to find a match

       Last metadata expiration check: 0:00:04 ago on Sat 19 Oct 2019 11:30:12 AM UTC.

       Package bzip2-1.0.6-26.el8.x86_64 is already installed.

       Package file-5.33-8.el8.x86_64 is already installed.

       Package findutils-1:4.6.0-20.el8.x86_64 is already installed.

       Package git-2.18.1-3.el8.x86_64 is already installed.

       Package gzip-1.9-4.el8.x86_64 is already installed.

       Package sudo-1.8.25p1-4.el8.x86_64 is already installed.

       Package tar-2:1.30-4.el8.x86_64 is already installed.

       Package which-2.21-10.el8.x86_64 is already installed.

       Package unzip-6.0-41.el8.x86_64 is already installed.

       Package xz-5.2.4-3.el8.x86_64 is already installed.

       Package zip-3.0-23.el8.x86_64 is already installed.

       No match for argument: libselinux-python

       Error: Unable to find a match

[balous]

Recently released Ubuntu Focal doesn't contain python-pip, there is just python3-pip.