move changes from dockerfile to template

templates/tools/dockerfile/test/cxx_wheezy_x64/Dockerfile.template

@@ -41,6 +41,12 @@
     g++-4.4 ${'\\'}
     g++-4.4-multilib
 
+  # set up backport to allow installation of Git version > 1.7
+  RUN echo "deb http://http.debian.net/debian wheezy-backports main" \
+    >/etc/apt/sources.list.d/wheezy-backports.list
+  RUN apt-get update -qq
+  RUN apt-get -t wheezy-backports install -qq git
+  
   RUN wget ${openssl_fallback.base_uri + openssl_fallback.tarball}
 
   ENV POST_GIT_STEP tools/dockerfile/test/cxx_wheezy_x64/post-git-setup.sh

tools/dockerfile/test/cxx_wheezy_x64/Dockerfile

@@ -63,13 +63,6 @@ RUN apt-get update && apt-get install -y \
 # Build profiling
 RUN apt-get update && apt-get install -y time && apt-get clean
 
-#================
-# Add backport to Debian sources.list and update git to version > 1.7
-RUN echo "deb http://http.debian.net/debian wheezy-backports main" \
-  >/etc/apt/sources.list.d/wheezy-backports.list
-RUN apt-get update -qq
-RUN apt-get -t wheezy-backports install -y -qq git mercurial
-
 #====================
 # Python dependencies
 
@@ -96,6 +89,11 @@ RUN apt-get update && apt-get install -y \
   g++-4.4 \
   g++-4.4-multilib
 
+# set up backport to allow installation of Git version > 1.7
+RUN echo "deb http://http.debian.net/debian wheezy-backports main"   >/etc/apt/sources.list.d/wheezy-backports.list
+RUN apt-get update -qq
+RUN apt-get -t wheezy-backports install -qq git
+
 RUN wget https://openssl.org/source/old/1.0.2/openssl-1.0.2f.tar.gz
 
 ENV POST_GIT_STEP tools/dockerfile/test/cxx_wheezy_x64/post-git-setup.sh