libchromeos: add support for synchronous PropertySet::Set to dbus

This CL adds the support for the newly added SetAndBlock function
in libchrome dbus library.
This will allow us to use a synchronous version of PropertySet::Set.

Bug: 24131409
TEST=run tests on a veyron_jaq chromebook

Change-Id: I1bf14e187e69fbc128bb0c696557575fbf6f22fa
1 file changed