Abstracted the lldb-specific unittest.TestCase.setUp()/tearDown() in a separate

module lldbtest.py and refactored the existing test cases to derive from the
abstract base class lldbtest.TestBase.

MOdified the test driver (dotest.py and dotest.pl) to set up additional
PYTHONPATH component for locating the lldbtest module, which sits in the same
directory.

llvm-svn: 107563