[Reproducers] Initialize reproducers before initializing the debugger.

As per the discussion on the mailing list:
http://lists.llvm.org/pipermail/lldb-commits/Week-of-Mon-20190218/048007.html

This commit implements option (3):

> Go back to initializing the reproducer before the rest of the debugger.
> The method wouldn't be instrumented and guarantee no other SB methods are
> called or SB objects are constructed. The initialization then becomes part
> of the replay.

Differential revision: https://reviews.llvm.org/D58410

llvm-svn: 354631