Add display of cpu info (#1010)

I had originally catted /proc/cpuinfo but it was very verbose

lscpu is in util-linux which is in essential so should be available on systems.

ros_buildfarm/templates/snippet/builder_shell_docker-info.xml.em

@@ -1,6 +1,9 @@
 @(SNIPPET(
     'builder_shell',
     script='\n'.join([
+        'echo "# BEGIN SECTION: cpu info"',
+        'lscpu',
+        'echo "# END SECTION"',
         'echo "# BEGIN SECTION: docker version"',
         'docker version',
         'echo "# END SECTION"',