[autotest] GenericHostRunError.

Renamed HostRunErrorMixIn to GenericHostRunError as a generic
error used for both client and server host.run failures. Fixed ADBHost,
EmulatedADBHost, EmulatorManager and all android/brillo tests to catch this
exception where they were catching one or both of AutotestHostRunError and
AutoservRunError.

TEST=Verified locally, ran unit tests.
BUG=None

Change-Id: I87e166bd580df7dd4b021e2fe0b426beaba2c270
Reviewed-on: https://chromium-review.googlesource.com/367015
Commit-Ready: Justin Giorgi <jgiorgi@google.com>
Tested-by: Justin Giorgi <jgiorgi@google.com>
Reviewed-by: Dan Shi <dshi@chromium.org>
diff --git a/utils/emulator_manager.py b/utils/emulator_manager.py
index 470767a..395d521 100644
--- a/utils/emulator_manager.py
+++ b/utils/emulator_manager.py
@@ -38,7 +38,7 @@
                                             'between 5555 and 5585.')
         try:
             run('test -f %s' % os.path.join(imagedir, 'system.img'))
-        except (error.AutoservRunError, error.AutotestHostRunError):
+        except error.GenericHostRunError:
             raise EmulatorManagerException('Image directory must exist and '
                                            'contain emulator images.')