[LIT] Have lit run the lldb test suite

This is the first in what will hopefully become a series of patches to
replace the driver logic in dotest.py with LIT. The motivation for this
change is that there's no point in maintaining two driver
implementations. Since all of the LLVM projects are using lit, this is
the obvious choice.

Obviously the goal is maintain full compatibility with the functionality
offered by dotest. As such we won't be removing anything until that
point has been reached.

This patch is the initial attempt (referred to as v1) to run the lldb
test suite with lit. To do so we introduced a custom LLDB test format
that invokes dotest.py with a single test file.

Differential revision: https://reviews.llvm.org/D45333

llvm-svn: 330275