Fix various adb error reporting bugs.

`adb install` was writing success to stderr rather than stdout.

Server mismatch messages were going to stdout rather than stderr.

Error messages should consistently start with a lower case letter.

Also improve consistency of syntax error reporting.

Bug: https://issuetracker.google.com/37128706 (adb install success to stdout)
Bug: https://issuetracker.google.com/37140458 (server mismatch on stderr)
Bug: http://b/32413861 (consistency)
Test: ran tests
Change-Id: I0d6cb0c7482bec03483dacefd996644b7a28d273
diff --git a/adb_utils.h b/adb_utils.h
index e0ad103..c1d5549 100644
--- a/adb_utils.h
+++ b/adb_utils.h
@@ -21,7 +21,7 @@
 
 #include <android-base/macros.h>
 
-int usage(const char*, ...);
+int syntax_error(const char*, ...);
 
 void close_stdin();