Use 'pip' consistently for installing buildbot-slave from PyPI (#155)
Use 'pip' consistently for installing buildbot-slave from PyPI (#155)

With CentOS/RHEL; Fedora; and SUSE, we were using 'easy_install'
to install buildbot-slave instead of 'pip'. However, 'easy_install'
was failing to install with the latest CentOS 7 official images.

However, it does install correctly when using 'pip', but that
requires having EPEL activated at bootstrap phase for CentOS/RHEL.
Consequently, EPEL is now installed and appropriately configured.

In addition, there's a trivial change to fix the Fedora bootstrap
such that installation of buildbot-slave comes from PyPI for
Fedora 28+, since the buildbot-slave package was replaced by
buildbot-worker from buildbot 1.x.

Signed-off-by: Neal Gompa <29fda311c4efe6c7641a4bc7ee8d8312a3ce088e@datto.com>
zfsonlinux/zfs-buildbot,zfsonlinux/zfs-buildbot