Correct md5sum executable on OSX hosts

On OSX hosts the md5sum executable is called md5 instead.

Change-Id: I0b8e3ab137136be6e45fd4b9f77f2c036e8b981a
migrate: fix merge fail

Change-Id: Ic7caec90cd2c7bb977040d4e416016ca36ee4eea
u1: import from CyanogenMod/android_kernel_samsung_smdk4210

Change-Id: I9629a4060538c9c4c6a43a86a56826cd7123d1b5