Rotating a Group of Vectors

Construct 4×4 transform matrix instead of Quaternions.

Do not forget that OpenGL has column wise matrix

so for double m[16];

is X axis vector in m[ 0],m[ 1],m[ 2]

is Y axis vector in m[ 4],m[ 5],m[ 6]

is Z axis vector in m[ 8],m[ 9],m[10]

and position is in m[12],m[13],m[14]

The LCS mean local coordinate system (your triangle or object or whatever)
and GCS mean global coordinate system (world or whatever).

All the X,Y,Z vectors should be normalized to unit vectors otherwise scaling will occur.
construction
1. set Z-axis vector to your triangle normal
2. set position (LCS origin) to mid point of your triangle (or average point form its vertexes)
3. now you just need X and Y axises which is easy
  
  let X = any triangle vertex - triangle midpoint
  
  or X = substraction of any 2 vertexes of triangle
  
  The only condition that must be met for X is that it must lie on triangle plane.
  
  Now let Y = X x Z the cross product will create vector perpendicular to X and Z (which also lies in triangle plane).
4. now put all this inside matrix and load it to OpenGL as ModelView matrix or what ever.