doc: Solved sphinx-build import errors.

Added _static folder to remove a sphinx-build warning,
removed obsolete SPM.rst, updated doc Makefile it now
exports the PYTHONPATH, before doc generation create_sl
is invoked and adds a symbolic link to vdscli.py in the
vdsm python package if it's missing. Reduced warnings
with :noindex: directive.

Change-Id: I836210fa5bbd844c20b3b5444be24cd9fa4023e2
Signed-off-by: Giuseppe Vallarelli <giuseppevallarelli@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/11652
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>