Optional Full Disk Encryption (Close #86)

Created by: ollieparanoid

I have created a new branch, because I made the mistake of putting two features in the old branch (optional FDE and boot.img creation in mkinitfs), so it became quite unreadable.

Anyway, here is the clean version, with only the optional FDE feature.

@MartijnBraam, @PabloCastellano: Could you please test this PR on your devices?

I've tested it on the i9100 in the following configurations:

• fde + usb-shell hook
• fde
• no-fde
• no-fde + usb-shell hook (this will only be useful, if switch_root fails, because telnet won't work after that)

Changes:

• --no-fde Parameter
• pmOS root partition gets assigned a label now
• initfs code handles unencrypted root partitions, too
• rewrote find_root_partition to make it compatible with the i9100 again (and added a big description comment about how it works)
• usb network and dhcp server gets started independent of hooks now. this really makes sense for development now, we can disable this later (and set up networking via OpenRC, when the usb-shell hook is not installed)
• telnet splash + unlock telnetd code only runs, when the rootfs is encrypted
• usb_setup_android wrapped with a generic usb_setup function, so we can support networking for more device types in a clean way
• the IP of the device is now in init_functions.sh, and init_functions.sh gets included in all hooks.
• rewrote logging function. it logs all stdout and stderr to /pmOS_init.log, except when PMOS_NO_OUTPUT_REDIRECT is specified as kernel command line. This way we can see error output from all commands.
• used shfmt to format everything, so it looks consistent again
• added automatic shellchecking for init.sh.in and init_functions.sh
• clear naming scheme for initfs functions, they all start with a verb now (e.g. setup_usb_network, start_udhcpd, ...)