Set --python when running sytest

.. because I want to make the 'install_and_run' script useful for non-synapse
jobs, which do not accept --python. In any case we set up the path here, so
sytest shouldn't be guessing it.

jenkins-dendron-haproxy-postgres.sh

@@ -17,6 +17,7 @@ export HAPROXY_BIN=/home/haproxy/haproxy-1.6.11/haproxy
 ./sytest/jenkins/prep_sytest_for_postgres.sh
 
 ./sytest/jenkins/install_and_run.sh \
+    --python $WORKSPACE/.tox/py27/bin/python \
     --synapse-directory $WORKSPACE \
     --dendron $WORKSPACE/dendron/bin/dendron \
     --haproxy \

jenkins-dendron-postgres.sh

@@ -15,5 +15,6 @@ export SYNAPSE_CACHE_FACTOR=1
 ./sytest/jenkins/prep_sytest_for_postgres.sh
 
 ./sytest/jenkins/install_and_run.sh \
+    --python $WORKSPACE/.tox/py27/bin/python \
     --synapse-directory $WORKSPACE \
     --dendron $WORKSPACE/dendron/bin/dendron \

jenkins-postgres.sh

@@ -14,4 +14,5 @@ export SYNAPSE_CACHE_FACTOR=1
 ./sytest/jenkins/prep_sytest_for_postgres.sh
 
 ./sytest/jenkins/install_and_run.sh \
+    --python $WORKSPACE/.tox/py27/bin/python \
     --synapse-directory $WORKSPACE \

jenkins-sqlite.sh

@@ -12,4 +12,5 @@ export SYNAPSE_CACHE_FACTOR=1
 ./jenkins/clone.sh sytest https://github.com/matrix-org/sytest.git
 
 ./sytest/jenkins/install_and_run.sh \
+    --python $WORKSPACE/.tox/py27/bin/python \
     --synapse-directory $WORKSPACE \