tools, ospfclient: add a config option to skip installing python scripts

tools, ospfclient: add a config option to skip installing python scripts

The new config option --disable-python-runtime allows make install to proceed
without installing any of the python scripts. When installing from deb/rpm
packages those are bundled as frr-pythontools, which is independent from the
frr binaries and can already be skipped. I.e, this PR gives the option to skip
those scripts when building/installing from sources too.

Signed-off-by: Jafar Al-Gharaibeh <jafar@atcorp.com>