Rename libkeymaster to libkeymaster_staging

Fix a build breakage by renaming libkeymaster to
libkeymaster_staging. fugu's vendor tree already had
a libkeymaster.so which masked system/keymaster/libkeymaster.

Bug: 37997750
Change-Id: Iead014db3f3d841f08c8072b0493ec9fd7a05055
diff --git a/trusty/keymaster/Android.mk b/trusty/keymaster/Android.mk
index 47c17bd..5d2f642 100644
--- a/trusty/keymaster/Android.mk
+++ b/trusty/keymaster/Android.mk
@@ -38,7 +38,7 @@
 	libcrypto \
 	libcutils \
 	libkeymaster_portable \
-	libkeymaster \
+	libkeymaster_staging \
 	libtrusty \
 	libkeymaster_messages \
 	libsoftkeymasterdevice \