gummiboot-postinst.sh: create loader/loader.conf and code beauty
gummiboot-postinst.sh: create loader/loader.conf and code beauty

if loader/loader.conf does not exist, create it with

default *$ID*

where $ID is the distro ID in /etc/os-release.

Also turned all variables in upper case.

aaronp24/gummiboot,miguelinux/gummiboot2systemd-boot,aaronp24/gummiboot,karelzak/gummiboot,todorez/tummiboot,android-ia/platform_external_gummiboot,miguelinux/gummiboot2systemd-boot,android-ia/platform_external_gummiboot,FrozenCow/gummiboot,todorez/gummiboot-multiboot2,FrozenCow/gummiboot,liliang365/my_gummiboot,trilean/gummiboot,liliang365/my_gummiboot,karelzak/gummiboot,trilean/gummiboot,freedesktop-unofficial-mirror/gummiboot,todorez/tummiboot,freedesktop-unofficial-mirror/gummiboot,todorez/gummiboot-multiboot2