Fixed Makefile-based install to place python packages in the LLDB install tree.
Failure to install python packages now fails the make install.
This patch properly handles the optional DESTDIR variable.

Patch by Todd Fiala



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@196624 91177308-0d34-0410-b5e6-96231b3b80d8