grub: Use bootloaderEntryName instead of shortProductName.

Use bootloaderEntryName instead of shortProductName as the
--bootloader-id.
grub/test.yaml: Simulate bootloaderEntryName instead of shortProductName.

That is what grub/main.py now expects in the global storage.
Fix unpackfs wrongly excluding separately-mounted partitions.

mount: Remember the extraMounts (and extraMountsEfi, if applicable) in
the global storage (as "extraMounts").

unpackfs: Read the extra mounts from the global storage to generate the
exclude list instead of trying to detect it from the "mount" command's
output, because the latter also includes normally-mounted destination
partitions.

This makes having separate partitions for non-/ mountpoints work again.
unpackfs: Fix error in list_excludes.

I accidentally removed the initialization of lst.
grub: Add an optional efiBootloaderId setting.

If the efiBootloaderId is set, it is used as the --bootloader-id when
installing grub-efi. The rationale is pretty much the same as for the
Gummiboot case.

If the setting is not used, the --bootloader-id is determined from the
branding's bootloaderEntryName (as before).
Merge pull request #56 from calamares/master

Merge master