Mount tmpfs on /cores

Proper selinux labeling support for files on rootfs was
never completely implemented. Instead of putting coredump
files on rootfs, put them on tmpfs instead.

See: http://www.mail-archive.com/seandroid-list@tycho.nsa.gov/msg01815.html

Bug: 18227650
Change-Id: I2eeabee4fe1a14bfbf990a4a518d538d6b4b6e87

envsetup.sh

@@ -911,6 +911,7 @@ function coredump_setup()
 	sleep 1;
 	adb wait-for-device;
 	adb shell mkdir -p /cores;
+	adb shell mount -t tmpfs tmpfs /cores;
 	adb shell chmod 0777 /cores;
 
 	echo "Granting SELinux permission to dump in /cores...";