fix getting pip for python3.5

templates/tools/dockerfile/test/python_stretch_3.5_x64/Dockerfile.template

@@ -17,4 +17,4 @@
   <%include file="../../python_stretch.include"/>
 
   RUN apt-get update && apt-get install -y python3.5 python3-all-dev
-  RUN curl https://bootstrap.pypa.io/get-pip.py | python3.5
+  RUN curl https://bootstrap.pypa.io/3.5/get-pip.py | python3.5

templates/tools/dockerfile/test/python_stretch_default_x64/Dockerfile.template

@@ -19,7 +19,7 @@
   <%include file="../../compile_python_38.include"/>
 
   RUN apt-get update && apt-get install -y python3.5 python3.5-dev
-  RUN curl https://bootstrap.pypa.io/get-pip.py | python3.5
+  RUN curl https://bootstrap.pypa.io/3.5/get-pip.py | python3.5
 
   RUN apt-get update && apt-get -t buster install -y python3.7 python3-all-dev
   RUN curl https://bootstrap.pypa.io/get-pip.py | python3.7