If I set the value of swappiness to 100 and try to boot ubuntu installed harddrive in my friend's computer that does not have RAM, can I boot the computer without Ram at all?
No. The CPU can't execute code from the swap. Swapping works by moving RAM contents to the disk and other disk contents to RAM, but execution is always from RAM.
And no, there is no way to transfer code or data from the disk directly to the CPU caches. You can't bypass the RAM.
Even microcontroller architectures that can execute code directly from NOR flash need RAM for the stack, at least some built-in SRAM as some controllers have.
https://electronics.stackexchange.com/a/311839/111920 contains the link http://www.drdobbs.com/parallel/booting-an-intel-architecture-system-par/232300699?pgno=2 which describes the boot process of a modern Intel CPU in excruciating detail.
TL;DR: No. There indeed is a phase during boot where the RAM chips are not used, and the processor is running with only its internal cache functioning as makeshift RAM. But this is very early in the BIOS load process and one of the first things the BIOS does is initialize the RAM, to be able to use it. The machine code running there is very specialized, very hand-crafted.
After that very early stage, RAM is needed for everything. This means that you won't even be able to go into BIOS, get a video signal, or much less boot from any medium, without RAM.