[TestEvents] Replace expectedFailureLinux with skipIfLinux

Summary:
If we do not mark them as skip, they are still executed, which in
turn is leading to an assertion failure. The change also adds
skipIfLinux to a testlet which was not previously marked with
skipIfLinux. This is because running even that test let leads to an
assertion failure.

Test Plan: dotest.py -C clang -p TestEvents.py

Reviewers: vharron

Reviewed By: vharron

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D6715