Use shell to execute commands inside docker container as a buggy docker-py client exec_start api sometimes hangs.
Also fix the test container scapy and scapy-ssl_tls versions

Change-Id: I2cc3a22f8d4143253caaa2f26ab5c27afd365c41
(cherry picked from commit ec5b72a16ee6b72f7bacaeaeacd71094ec53c4dc)
diff --git a/Dockerfile.tester b/Dockerfile.tester
index e47ccff..966f45b 100644
--- a/Dockerfile.tester
+++ b/Dockerfile.tester
@@ -16,7 +16,7 @@
  cd openvswitch-2.5.0 && \
  ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var --disable-ssl && make && make install)
 RUN service openvswitch-switch restart || /bin/true
-RUN pip install -U scapy scapy-ssl_tls monotonic configObj docker-py pyyaml nsenter pyroute2 netaddr python-daemon
+RUN pip install scapy==2.3.2 scapy-ssl_tls==1.2.2 monotonic configObj docker-py pyyaml nsenter pyroute2 netaddr python-daemon
 RUN mv /usr/sbin/tcpdump /sbin/
 RUN ln -sf /sbin/tcpdump /usr/sbin/tcpdump
 RUN mv /usr/sbin/dhcpd /sbin/