[Test Suite] Properly respect --framework option

Summary:
dotest.py has a framework option that is not respected. This patch makes the framework path properly configurable via the --framework option.

This patch also adds a function to the lldbtest.Base class named "hasDarwinFramework" which allows us to not rely on the host platform to determine if a framework is present. If running on Darwin, and not building a framework, this will follow the *nix code paths which are appropriate for Darwin.

Reviewers: tfiala

Subscribers: lldb-commits, mgorny

Differential Revision: https://reviews.llvm.org/D25886

llvm-svn: 285541