Improve python modules detection

Improve python modules detection

After I tried to build libabigail on Debian, I realized the detection
of python modules wasn't that great.  The koji module wasn't present
and yet the detection system tried to launch fedabipkgdiff regression
tests.  Woops.

I was thinking about coming up with something easier to to update to
add new modules to check for anyway, so I just dived in.  I came up
with a new autoconf macro of my own, AX_CHECK_PYTHON_MODULES, that
lets you check for the presence of several python modules at once.
This is more handy than having to call AX_PYTHON_MODULE for each
module we want to detect.  This fixes the detection issue I found and
simplifies configure.ac.

	* configure.ac: Include
	autoconf-archive/ax_check_python_modules.m4 rather than
	autoconf-archive/ax_python_module.m4.  Use AX_CHECK_PYTHON_MODULES
	rather than AX_PYTHON_MODULE.
	* Makefile.am: Add the new file
	autoconf-archive/ax_check_python_modules.m4 to source distribution
	and remove the older autoconf-archive/ax_python_module.m4 one.
	* autoconf-archive/ax_check_python_modules.m4: New file.
	* autoconf-archive/ax_python_module.m4: Remove.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>