[dotest] Centralize initialization commands even more

Summary:
In r367234 we introduced a central place to hold the set up commands for
the various ways we have of launching lldb. However, a number of
commands still remained outside of that.

This patch moves the remaining set up commands into this function, which
allows us to remove manual clang module path setting code in
TestBatchMode.

One unfortunate victim of this approach is TestSTTYBeforeAndAfter which,
due to how it launches lldb (pexpect->expect->lldb), fails get the
quoting right. It would be possible to fix the quoting there, it would be a bit
icky, and none of the commands in this list are really relevant for what this
test is doing, so I just remove the commands outright.

Reviewers: JDevlieghere, jankratochvil

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D67173

llvm-svn: 371019