Fix CI issues

[roman-dvorak]

This PR solves two of the three problems with CI. Fixes an issue on version 3.4 and 3.5 where there was an unnecessary break in the if and elif functions and exit() instead of sys.exit().

In version 2.7 there is still issue

E: 88,12: Assigning to function call which doesn't return (assignment-from-no-return)

from line:

pitch = np.arcsin(2.0 * (q[0] * q[2] - q[3] * q[1]))

It can be related to pylint bug: pylint-dev/pylint#2694

But will python 2.7 be further supported? Official support of python 2.x ends on January 1.

[bkueng]

Thanks. You're right, I removed python 2 from CI in 5835c86

[roman-dvorak]

break-elif mistake was repaired.