Imu test - review the error check

[martinaxgloria]

This PR aims to fix the way the error between the expected values and the measured ones is computed during the IMU orientation test. In details:

• starting from the rotation matrices of the expected and measured orientation values, the axis-angle representation is used to compute the error as the magnitude of the vector representing the rotation axis;
• during the whole trajectory, the error is computed at every moment and stored;
• the maximum value of error is compared with the reference value defined for the test, and so to determine if the test is passed or failed.

cc @pattacini