Add yum-utils to the CentOS 7 image (for needs-restarting)

[lpancescu]

No description provided.

[jperrin]

Why is this needed in the base container?

[lpancescu]

Because of needs-restarting, which is essential when performing yum updates, to decide which services need to be restarted (even if it doesn't cover cases when a reboot would be advisable). The CentOS 6 image provides needs-restarting by default, it would also be nice to be consistent - not sure why it was omitted in CentOS 7.

We already have screen, man-pages and bash-completion in the base container, whose presence is even harder to justify than needs-restarting (especially for mostly non-interactive usage). Ideally, we'd have a minimal image, only adding the packages that Vagrant requires to bring the machine up, e.g. rsync and nfs-utils, with everything else handled directly by users via provisioning. I think this is what Fedora Cloud does, and the approach I'd prefer. But not everyone agrees with that point of view, and we even have requests like issue #27, including the VirtualBox Guest Additions by default, which would also require the development tools, the kernel headers and the X11 libraries.