msvs.py: support for range of msvs versions
msvs.py: support for range of msvs versions

  * on the command line one can now say list a comma-separated list of
  MSVS/MSVC versions. For example: "--msvs-version 15,12".  This will
  ask mbuild to try to find and use dev 15 or dev 12 in that order. If
  neither version is found, it will die with an error.  Specifing one
  version without a comma is also fine.

  * this allows for older systems to use a permitted older compiler,
  and for newer systems to use a preferred compiler. Also allows for
  project compiler upgrades to be spread out in time so the builds
  continue to work (assuming porting to new compiler was done and does
  not break the older compilers' compililations).

Change-Id: I7dd44d5277cfbc787a22f6f3a1bee6300f35bb5d
(cherry picked from commit 3f77f505167db81e90f11e335aabfca02685df5d)

intelxed/mbuild,intelxed/mbuild,intelxed/mbuild