build: Change --with-febootstrap-yum-config to --with-febootstrap-packager-config

For the rationale behind this renaming, see:
https://github.com/libguestfs/febootstrap/commit/b8cbe191d0f03af1f6a42a07795995b16d5a8c24

You can still, for the time being, use
./configure --with-febootstrap-yum-config
but it's preferred to switch to the new option.  The new option is
identical, just renamed.

Qe still pass the deprecated --yum-config option to febootstrap
itself, since both old and new febootstrap support this.
(cherry picked from commit bfddae7ceefa4a419ff56848122a46c71c4d6a3c)
Use 'supermin' and 'supermin-helper' in preference to febootstrap.

Febootstrap has been renamed upstream to 'supermin':
https://www.redhat.com/archives/libguestfs/2013-February/msg00004.html

This commit changes libguestfs so it can use either program to build
the supermin appliance.

(cherry picked from commit a0a4ee5245afdb7961d39b243439b902229dd599)
RHEL 7: Switch ruby to use vendor instead of site directory.
RHEL 7: Emphasize libguestfs-winsupport package (RHBZ#627468).

This RHEL-only patch changes the error messages when the
inspection code cannot find an operating system inside the guest
image.  For a Windows guest this may happen because the user has not
installed the separate 'libguestfs-winsupport' package.  Therefore we
emphasize that the user may need to install this package.

Notes:

(1) In RHEL there are two pieces of inspection code, the old Perl code
(deprecated upstream) and the new C core inspection API.  Therefore
this patch has to touch two places with essentially the same change.

(2) This patch doesn't try to be clever and detect if it was a Windows
guest.  This should reduce the chance of failure.

Output from (Perl) virt-inspector now looks like this:

 $ virt-inspector disk.img
 No operating system could be detected inside this disk image.

 This may be because the file is not a disk image, or is not a virtual machine
 image, or because the OS type is not understood by virt-inspector.

 If you feel this is an error, please file a bug report including as much
 information about the disk image as possible.

 RHEL notice
 -------------
 libguestfs will return this error for Microsoft Windows guests if the
 separate 'libguestfs-winsupport' package is not installed. If the
 guest is running Microsoft Windows, please try again after installing
 'libguestfs-winsupport'.

Output from guestfish (ie. C core inspection API) now looks like this:

 $ guestfish -i disk.img
 guestfish: no operating system was found on this disk

 RHEL notice
 -------------
 libguestfs will return this error for Microsoft Windows guests if the
 separate 'libguestfs-winsupport' package is not installed. If the
 guest is running Microsoft Windows, please try again after installing
 'libguestfs-winsupport'.
RHEL 7: Remove libguestfs live (RHBZ#798980).

This isn't supported in RHEL 7.
RHEL 7: Exclude iptables from the appliance (RHBZ#858648).
RHEL 7: Ignore /etc/release if /etc/redhat-release exists (RHBZ#873219).

If the user has created /etc/release on a RHEL machine, don't
mis-detect the OS as NetBSD.