Fix compiler warnings in test wrapper generation

[BruceForstall]

There were lots of warnings like the following:

Loader.classloader.XUnitWrapper.cs(96333,37): warning CS0168: The variable 'ex' is declared but never used

[4creators]

@BruceForstall I am in middle of fixing these warnings and many others as well in PR #19109 and fix will be more comprehensive. If you woant to proceed with this PR let me know.

[BruceForstall]

@dotnet/dnceng "No space left on device"

https://ci.dot.net/job/dotnet_coreclr/job/master/job/x64_checked_ubuntu_corefx_innerloop_prtest/597/

13:05:50 Building remotely on ubuntu1404-20180321-3a0c01 (ubuntu1404-20180321) in workspace /mnt/j/workspace/dotnet_coreclr/master/x64_checked_ubuntu_corefx_innerloop_prtest
...
13:06:16 FATAL: Unable to produce a script file
13:06:16 Also:   hudson.remoting.Channel$CallSiteStackTrace: Remote call to ubuntu1404-20180321-3a0c01
13:06:16 		at hudson.remoting.Channel.attachCallSiteStackTrace(Channel.java:1693)
13:06:16 		at hudson.remoting.UserResponse.retrieve(UserRequest.java:310)
13:06:16 		at hudson.remoting.Channel.call(Channel.java:908)
13:06:16 		at hudson.FilePath.act(FilePath.java:986)
13:06:16 		at hudson.FilePath.act(FilePath.java:975)
13:06:16 		at hudson.FilePath.createTextTempFile(FilePath.java:1363)
13:06:16 		at hudson.tasks.CommandInterpreter.createScriptFile(CommandInterpreter.java:162)
13:06:16 		at hudson.tasks.CommandInterpreter.perform(CommandInterpreter.java:94)
13:06:16 		at hudson.tasks.CommandInterpreter.perform(CommandInterpreter.java:66)
13:06:16 		at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
13:06:16 		at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:744)
13:06:16 		at hudson.model.Build$BuildExecution.build(Build.java:206)
13:06:16 		at hudson.model.Build$BuildExecution.doRun(Build.java:163)
13:06:16 		at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:504)
13:06:16 		at hudson.model.Run.execute(Run.java:1724)
13:06:16 		at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
13:06:16 		at hudson.model.ResourceController.execute(ResourceController.java:97)
13:06:16 		at hudson.model.Executor.run(Executor.java:429)
13:06:16 
java.io.IOException: No space left on device
13:06:16 	at java.io.FileOutputStream.writeBytes(Native Method)
13:06:16 	at java.io.FileOutputStream.write(FileOutputStream.java:326)
13:06:16 	at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221)
13:06:16 	at sun.nio.cs.StreamEncoder.implClose(StreamEncoder.java:316)
13:06:16 	at sun.nio.cs.StreamEncoder.close(StreamEncoder.java:149)
13:06:16 	at java.io.OutputStreamWriter.close(OutputStreamWriter.java:233)
13:06:16 	at hudson.FilePath$17.invoke(FilePath.java:1380)
13:06:16 	at hudson.FilePath$17.invoke(FilePath.java:1363)
13:06:16 	at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2760)
13:06:16 	at hudson.remoting.UserRequest.perform(UserRequest.java:207)
13:06:16 	at hudson.remoting.UserRequest.perform(UserRequest.java:53)
13:06:16 	at hudson.remoting.Request$2.run(Request.java:358)
13:06:16 	at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
13:06:16 	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
13:06:16 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
13:06:16 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
13:06:16 	at java.lang.Thread.run(Thread.java:748)
13:06:16 

[BruceForstall]

@4creators I can wait for your change. Is it going to happen soon? It looks like there's some controversy, and you haven't touched it in a few days.

[mmitche]

This particular machine had a tmp drive filled with core dumps. I think corefx's. I've deleted it.

[tannergooding]

The feedback on #19109 was to print the exception details here. #19109 (comment)

CC. @AaronRobinsonMSFT

[AaronRobinsonMSFT]

Yes, please print the exception itself. It costs very little but offers so much when reading the logs. Thanks @tannergooding !

[4creators]

@BruceForstall I will push new commits today if it's OK

[4creators]

@BruceForstall This can be closed as #19180 is merged.