bootstrap: Use toolchain finder of vita-header repo

[d3m3vilurr]

this patch requires python.
IDK default python version in OSX (might be not installed in vanilla
system)

this patch will replace #43

[yne]

Confirmed working fine here (Ubuntu 18.04.1 LTS, Python 2.7.15rc1)

If you need some inspiration for any future unifying/refactoring: the following line works fine, does not use curl, does not spawn a subshell $(...), and does not produce any temporary garbage:

wget -qO- github.com/vitasdk/vita-headers/raw/master/.travis.d/last_built_toolchain.py|\
python - master linux | xargs wget -qO- | tar xjf - -C tmp --strip-components=1

Just to be sure : We do all of this hassle to avoid consuming the made-for-this-kind-of-stuff-API quota ?

[d3m3vilurr]

yes, I also know that :)
and we should think multiple points

1. curl vs wget
   in my case, I prefer curl than wget, but some linux distro doesn't install the curl as default. btw (if i'm correct,) osx doesn't have wget in vanilla environ
2. github api limit
   inb4 we already got the github api quota problem in vita-header project. so we refactored direct use the release web page instead calling the release api
   imo, vita-header project would be reduced api/web page call. so current time would be better than before.
3. increase dependency
   many linux distro is installed python as default for the using their package system and some system tool. but windows doesn't. maybe osx also too.
   so best option is making the static linked tool using go/rust/c/c++
   but this approach of the patch would be quite difficulty in normal bash.
   I don't think so that python is optional dependency in general programmer group, but it just my thinking.
4. remove sudo
   i don't want to call sudo in normal env Fixed: Removed Sudo #23 Improve update script #27

[d3m3vilurr]

also @Rinnegatamante said he can't test this; his current python env is messed up ;)
so I just commit the this patch, and I'll think making the dedicated tool or port to bash script