CPS BuildProject.cs should log build result exception if any

[KirillOsenkov]

DevDiv 362186

In the code here:
http://index/?leftProject=Microsoft.VisualStudio.ProjectSystem&leftSymbol=gqgqt9etcoqs&rightProject=Microsoft.VisualStudio.ProjectSystem.Implementation&file=Build%5CBuildProject.cs&line=578

it is possible that result.Exception is not null (there was an exception during build).

CPS should check the result.Exception and if it's not null, log exception.ToString() to the errorTraceLogger.

The fact that this exception gets lost otherwise makes it super hard to debug design-time build failures. The log just says BUILD FAILED and that's it.

"Doesn't meet the bar"