Exec: take EchoOff into account when command fails (#5962)
Exec: take EchoOff into account when command fails (#5962)

According to documentation, "If [EchoOff is] true, the task will not emit the expanded form of Command to the MSBuild log."

This implements that if EchoOff is true by replacing it with an ellipsis and not echoing the command.
AndyGerlicher/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild,rainersigwald/msbuild,mono/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,mono/msbuild,mono/msbuild,rainersigwald/msbuild,mono/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild