Buildbot: improve 'Build MSVC_x64'

Improve the build script in the following way:

Reorder the build targets:

1. bootcdregtest
2. rostests
3. bootcd
4. livecd

Change CMake configuration:

• All targets: Only include en-US: '-DI18N_LANG="en-US"
• rostests: Do not reconfigure to avoid recompilation