[dotest] make debug info variant accessible in setUp()

[dotest] make debug info variant accessible in setUp()

Summary:
This changes the way we store the debug info variant to make it
available earlier in the test bringup: instead of it being set by the
test wrapper method, it is set as a *property* of the wrapper method.

This way, we can inspect it as soon as self.testMethodName is
initialized. The retrieval is implemented by a new function
TestBase.getDebugInfo(), and all that's necessary to make it work is to
change self.debug_info into self.getDebugInfo().

While searching for debug_info occurences i noticed that TestLogging is
being replicated for no good reason, so I removed the replication there.

Reviewers: aprantl, jingham

Subscribers: eraman, JDevlieghere, lldb-commits

Differential Revision: https://reviews.llvm.org/D42836

llvm-svn: 324226