Only trigger exits for pending IO in emulation.

Do not leave the loop over all VCPUS if we're currently in
simulating, or we risk confusing MARSS and asserting out.

Signed-off-by: Tyler Stachecki <tstache1@cs.binghamton.edu>
Leave inner main_loop faster on pending requests

If there is any pending request that requires us to leave the inner loop
if main_loop, makes sure we do this as soon as possible by enforcing
non-blocking IO processing.

At this change, move variable definitions out of the inner loop to
improve readability.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Conflicts:
	vl.c

As in the last commit, only take this action if we're not simulating.
Moreover, fix a few code-related formatting issues in this commit.

Signed-off-by: Tyler Stachecki <tstache1@cs.binghamton.edu>