Pass exitCode by reference

Arguments to defer statements are evaluated when the defer statement is
evaluated, so pass exitCode by reference instead.

Fixes issue #346
Remove test code duplication
Fix style issue in remote_exec_test
Also change the call sites. *sigh*
Merge pull request #349 from SnehaM/master

removed repeated 'can' Watches documentation
Merge pull request #347 from sorenh/remote_exec_exit_code

agent: Pass exitCode by reference
Go format fix
UI fix for OS X when having scrollbars `always on`

Resolves #343.
Hide vertical scrollbar in Safari