apmanager: Rename "chromeos" -> "brillo" in include paths and namespaces

libchromeos is transitioning to libbrillo and chromeos namespaces
and include directory is changing to brillo.

Bug: 24872993
TEST=built for aosp and brillo, all unit tests pass on dragonboard
Change-Id: I4c6efbc5bbf80d251e5d91bc3db49f02bc0e4732
diff --git a/process_factory.cc b/process_factory.cc
index 3f5e476..4517c6e 100644
--- a/process_factory.cc
+++ b/process_factory.cc
@@ -32,8 +32,8 @@
   return g_process_factory.Pointer();
 }
 
-chromeos::Process* ProcessFactory::CreateProcess() {
-  return new chromeos::ProcessImpl();
+brillo::Process* ProcessFactory::CreateProcess() {
+  return new brillo::ProcessImpl();
 }
 
 }  // namespace apmanager