configure.ac: build glupy with installed python

IOW with more than just python2.6. Python2.7 is certainly what's on
the vast majority of non-RHEL systems that are out there. Also our
rpm.t regression test will build on epel-5 under mock; RHEL5 has
Python2.4.

Change-Id: I09c95c1fb6b3498e910ad239c4f0af7f786c3700
BUG: 961856
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/5007
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>