grub2, os-prober: fixed issue with secureboot

This update fixes the following issue with grub2 and os-prober:
- grub2:
+ bnc#810912: recognize linuxefi/initrdefi too
- os-prober:
+ bnc#810912: use linuxefi in 30_os_prober if secure boot is enabled

Fixed bugs
bnc#810912
grub2-efi generates faulty commands for loading another linux (missing "initrd") in UEFI setup
Selected Binaries
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