gfapi.py: support dynamic loading of versioned libraries

Currently gfapi.py only loads libraries by filename ending in ".so".  On
an installed system without development packages, the <lib>.so filenames
are not available. ctypes.util.find_library() can be used to detect the
files dynamically.

In addition to this, also fixing some minor indention errors and package
the library into the Python site-packages path. Python applications and
libraries can now access libgfapi through 'from glusterfs import gfapi'.

Change and review in the master branch:
> Change-Id: I71e38dabd3ade5dcf24813bf2fc25cda91b571c6
> Signed-off-by: Niels de Vos <ndevos@redhat.com>
> Reviewed-on: http://review.gluster.org/5835
> Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>

BUG: 1005146
Change-Id: Id7665fe5140111be7bf2038454fb775c70b15993
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/6581
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>