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: Ie478726bf81e965be64fb913844b881064e9b66c
diff --git a/keymaster/3.0/default/Android.mk b/keymaster/3.0/default/Android.mk
index 2dbb200..87ad245 100644
--- a/keymaster/3.0/default/Android.mk
+++ b/keymaster/3.0/default/Android.mk
@@ -12,7 +12,7 @@
     libsoftkeymasterdevice \
     libcrypto \
     libkeymaster_portable \
-    libkeymaster \
+    libkeymaster_staging \
     libhidlbase \
     libhidltransport \
     libutils \