Propagate command interpreter errors from lldlbinit

This patch ensures that we propagate errors coming from the lldbinit
file trough the command/script interpreter. Before, if you did something
like command script import syntax_error.py, and the python file
contained a syntax error, lldb wouldn't tell you about it. This changes
with the current patch: errors are now propagated by default.

PS: Jim authored this change and I added testing.

Differential revision: https://reviews.llvm.org/D61579

llvm-svn: 360216
diff --git a/lldb/source/Target/Target.cpp b/lldb/source/Target/Target.cpp
index 5fbe33b..58f2325 100644
--- a/lldb/source/Target/Target.cpp
+++ b/lldb/source/Target/Target.cpp
@@ -2652,6 +2652,7 @@
         options.SetStopOnError(true);
         options.SetEchoCommands(false);
         options.SetPrintResults(true);
+        options.SetPrintErrors(true);
         options.SetAddToHistory(false);
 
         // Force Async: