Statsd namespace is defined and used

Statsd code now lives in android::os::statsd namespace. Existing files
are largely modified to follow this convention.

Exception: parse_util, since it seems a bit different.

Test: code compiles and existing statsd_tests still pass
Change-Id: Idf92a071b9ed172d01eb3087a4fa3609d67a038c
diff --git a/cmds/statsd/src/main.cpp b/cmds/statsd/src/main.cpp
index 161b630..c1dad4f 100644
--- a/cmds/statsd/src/main.cpp
+++ b/cmds/statsd/src/main.cpp
@@ -36,6 +36,7 @@
 #include <unistd.h>
 
 using namespace android;
+using namespace android::os::statsd;
 
 // ================================================================================
 /**