[vscode] Skip some of the vscode tests on Linux and fix one

Summary: These are already skipped on Darwin because they cause build bot failures. Both on the build bots as well as in our testing we have seen a number of these tests fail and hang. This change skips the failing/hanging tests on Linux and also fixes one of the test - the test needs the thread library to build.

Reviewers: asmith, clayborg, aprantl

Subscribers: teemperor, lldb-commits

Differential Revision: https://reviews.llvm.org/D51227

llvm-svn: 340658