- display warning if VS150COMNTOOLS is set to invalid path (#1802)
- display warning if VS150COMNTOOLS is set to invalid path (#1802)

* - display warning if VS150COMNTOOLS is set to invalid path

* - fix invalid variable usage

tivek/conan,tivek/conan,luckielordie/conan,luckielordie/conan,birsoyo/conan,conan-io/conan,conan-io/conan,memsharded/conan,lasote/conan,lasote/conan,memsharded/conan,birsoyo/conan,memsharded/conan,memsharded/conan,conan-io/conan