This is a backport of the patch for 'Bug#23713613: MTR DOES
NOT ALLOW VALGRIND TO BE RUN WITH CUSTOM TOOL'

Issue
=====
- MTR can not be run with --valgrind-option=--tool=<custom_tool>
  like massif/helgrind as it always adds the options for memcheck
  which can be invalid for other tools.
- The MTR --callgrind option does not work as it supplies an
  invalid callgrind argument '--base'.

Fix
===
- The patch restructures MTR to allow usage of the command line
  option --valgrind-option=--tool=<custom_tool> and removes the
  invalid option '--base' which was being supplied to callgrind.
- In addition, valgrind logs for tools like callgrind and massif
  are generated in the location <vardir>/log

Change-Id: I1b1e02061f3c029bb89818aee2f113f2b9effbfb