Moves CLI version suffix from preview1 to preview2
Sets channel for preview2 to 1.0.0-preview2, abandoning the Beta channel to the 1.0.0-preview1 release. Once @sokket's publishing cleanup work is complete we can re-converge the channels if desired.
In the MSI we used to check for any previous installation and we prevent any
installation of 'Release' version on top of 'Nightly' version and vice
versa. This is no longer needed since CLI SxS now. This is reminiscent of
pre-sharedFx CLI.
Fixes - #2467