EXO: Refactored remote shell interface

Move zcr_remote_shell interface out of server.cc
This CL only moves code around.

Bug: 896710
Test: Built on ChromeOS
Change-Id: I4ed019e376e5c374315c6bd5c0dab330588376f5
Reviewed-on: https://chromium-review.googlesource.com/c/1324092
Commit-Queue: Shawn Gallea <sagallea@google.com>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608675}
4 files changed