rfe11697: add prepareUpdate to python client

Added RepositoryConnection.prepareUpdate for sending
SPARQL 1.1 Update requests.

Tests added for:     rfe11697
make test-suite run? python-prepush

<release-note>
rfe11697: added RepositoryConnection.prepareUpdate

Added RepositoryConnection.prepareUpdate for SPARQL 1.1
Update requests. The call to evaluate on the returned UpdateQuery
object returns True or False.
</release-note>

<documentation>
Use RepositoryConnection.prepareUpdate for SPARQL 1.1
Update requests. The call to evaluate on the returned UpdateQuery
object returns True or False.
</documentation>

Change-Id: I78a45df8c890754c36cb71dfcda028c64ec3a5f3
Reviewed-on: https://gerrit.franz.com:9080/2382
Reviewed-by: John O'Rourke <jor@franz.com>
Reviewed-by: Ahmon Dancy <dancy@franz.com>
Tested-by: Kevin Layer <layer@franz.com>