build,win: try next MSVS version on failure
As suggested by @bnoordhuis in https://github.com/nodejs/node/pull/2843#discussion_r39415007 , vcbuild.bat
should try the next version of Visual Studio when VCINSTALLDIR
is not defined, as VC++ might not be installed for the current version.
This has already landed in v0.12 in e07c86e2.
cc @nodejs/platform-windows