[Reproducers] Change how reproducers are initialized.

[Reproducers] Change how reproducers are initialized.

This patch changes the way the reproducer is initialized. Rather than
making changes at run time we now do everything at initialization time.
To make this happen we had to introduce initializer options and their SB
variant. This allows us to tell the initializer that we're running in
reproducer capture/replay mode.

Because of this change we also had to alter our testing strategy. We
cannot reinitialize LLDB when using the dotest infrastructure. Instead
we use lit and invoke two instances of the driver.

Another consequence is that we can no longer enable capture or replay
through commands. This was bound to go away form the beginning, but I
had something in mind where you could enable/disable specific providers.
However this seems like it adds very little value right now so the
corresponding commands were removed.

Finally this change also means you now have to control this through the
driver, for which I replaced --reproducer with --capture and --replay to
differentiate between the two modes.

Differential revision: https://reviews.llvm.org/D55038

llvm-svn: 348152