Do not spam Sublime console when python does not contain robot

[stdedos]

There are a lot of open issues about errors related to python not having robot installed.

Instead of spamming the console, and sending "cryptic" error message to users, could it be a bit more specific?

It seems that the test from #201 is scriptable enough:

u@h:~$ robot/.venv/bin/python3 "from robot import run;run('--help')"
robot/.venv/bin/python3: can't open file 'from robot import run;run('--help')': [Errno 2] No such file or directory
u@h:~$ robot/.venv/bin/python3 -c "from robot import run;run('--help')"
[ ERROR ] Parsing '--help' failed: File or directory to execute does not exist.

Try --help for usage information.
u@h:~$ echo $?
0
u@h:~$ python -c "from robot import run;run('--help')"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: No module named robot
u@h:~$ echo $?
1

Could that be printed once per-plugin reload, instead of brute forcing and filling the console with first-failed error messages?

[aaltat]

Unfortunately I don't have time to solve this problem in the near seen future. But the code is in the repository and most likely this is not hard to do.