update_engine: 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
Change-Id: I770659a95be380a50fe3b2ba9f91d65818f40945
diff --git a/payload_generator/ext2_filesystem.cc b/payload_generator/ext2_filesystem.cc
index ff0bc37..182c098 100644
--- a/payload_generator/ext2_filesystem.cc
+++ b/payload_generator/ext2_filesystem.cc
@@ -317,7 +317,7 @@
   return true;
 }
 
-bool Ext2Filesystem::LoadSettings(chromeos::KeyValueStore* store) const {
+bool Ext2Filesystem::LoadSettings(brillo::KeyValueStore* store) const {
   // First search for the settings inode following symlinks if we find some.
   ext2_ino_t ino_num = 0;
   errcode_t err = ext2fs_namei_follow(
@@ -339,7 +339,7 @@
   if (err != 0)
     return false;
 
-  chromeos::Blob blob;
+  brillo::Blob blob;
   uint64_t physical_size = BlocksInExtents(extents) * filsys_->blocksize;
   // Sparse holes in the settings file are not supported.
   if (EXT2_I_SIZE(&ino_data) > physical_size)