shim: improve error messages
shim: improve error messages

%r when used in Print() will show a string representation of
an EFI_STATUS code.

Change-Id: I6db47f5213454603bd66177aca378ad01e9f0bd4
Signed-off-by: Andrew Boie <aab045b28152628be6af0e556050d0381fd0a34d@intel.com>

android-ia/platform_external_uefi_shim,rhinstaller/shim,rhinstaller/shim,CyanogenMod/android_external_uefi_shim,CyanogenMod/android_external_uefi_shim,android-ia/platform_external_uefi_shim,rhinstaller/shim,CyanogenMod/android_external_uefi_shim,android-ia/platform_external_uefi_shim