entity-manager: Add SkipDbusCreation field patch

This change adds a patch to support the SkipDbusCreation field in EM
configs. This field can be configured with a boolean value that controls
whether the dbus interface for the corresponding exposed field will be
created. The intention here is to provide an explicit field to disable
the dbus interface creation of sensors that will be fully supported and
exposed by tlBMC, therefore the dbus-sensor daemon will ignore the
config since it is never exposed over dbus.

This behavior is similar to the existing `"Status": 'disabled'` feature
available in entity-manager, but it prevents confusion to readers of the
EM config since the sensor is likely not disabled, just owned by tlBMC
instead of relying on dbus.

Google-Bug-Id: 517937319
Tested: https://paste.googleplex.com/4972037805309952
Fusion-Link:
platform15 http://fusion2/cba70619-fb41-3794-a9ee-08fa466ab3fe, Result: pass
platform11 http://fusion2/fe806f79-8c88-375f-b991-6c4a78cf4e14, Result: pass
Change-Id: Iadb0b59533edacd1226efd314e09d821e5e62e34
Signed-off-by: David Tang <davtang@google.com>