eng/common/tools.ps1 defaults are wrong

https://github.com/dotnet/arcade/blob/b5c8d9f6ae7c14af9e5e162e55201d41ebc191f5/eng/common/tools.ps1#L4-L52

All the `bool` switch conditions are always true even if the switch isn't supplied to the eng/common/build.ps1 file.

Example: `if (Test-Path variable:binaryLog)` is always true as `binaryLog` is defined as a `switch` which defaults to false and therefore Test-Path is always true.

This mainly affects to switches: `binaryLog` and `nodeReuse`. I assume that for that reason, these two got explicitly set in eng/common/build.ps1:

https://github.com/dotnet/arcade/blob/b5c8d9f6ae7c14af9e5e162e55201d41ebc191f5/eng/common/build.ps1#L153-L158

### Repro

Remove L153-158 from build.ps1 and run `./eng/common/build.cmd -ci`

This affects all custom entry point scripts which import tools.ps1, i.e. aspnetcore, roslyn, fsharp.