Description of problem:

There are a number of places where external commands are
run and on failure you get an error message like this:

*stdin*:4: libguestfs: error: external command failed, see earlier error messages

This message is confusing because:

(a) It doesn't tell you which external command failed.
(b) It doesn't say what we were trying to do.
(c) If debugging is not enabled, it is inaccurate -- there aren't
    any "earlier error messages"!

Version-Release number of selected component (if applicable):

libguestfs 1.20.4

How reproducible:

100%

Steps to Reproduce:

On Debian (which has old febootstrap), unpack libguestfs-1.20.4.tar.gz
and ./configure && make && make check.

It will fail with the line above, and no earlier error messages.

If you enable debugging then you'll see it's actually failing when
running febootstrap.