Restructured the reading of the high order grids for the FEM solver #8266

Job	Run time
Build SU2 (BaseMPI)	12m 53s
Build SU2 (ReverseMPI)	14m 5s
Build SU2 (asan) (BaseNoMPI-asan)	16m 42s
Build SU2 (ForwardMPI)	11m 31s
Build SU2 (asan) (ReverseNoMPI-asan)	44m 17s
Build SU2 (BaseNoMPI)	7m 50s
Build SU2 (tsan) (BaseOMP-tsan)	11m 52s
Build SU2 (ReverseNoMPI)	12m 48s
Build SU2 (tsan) (ReverseOMP-tsan)	27m 21s
Build SU2 (ForwardNoMPI)	10m 9s
Build SU2 (BaseOMP)	7m 48s
Build SU2 (ReverseOMP)	15m 2s
Build SU2 (ForwardOMP)	11m 12s
Unit Tests (test_driver)	1m 36s
Regression Tests (vandv.py)	2m 12s
Unit Tests (test_driver_AD)	52s
Regression Tests (tutorials.py)	6m 38s
Unit Tests (test_driver_DD)	59s
Regression Tests (parallel_regression.py)	14m 16s
Regression Tests (parallel_regression_AD.py)	9m 10s
Regression Tests (serial_regression.py)	16m 0s
Regression Tests (serial_regression_AD.py)	5m 11s
Regression Tests (hybrid_regression.py)	10m 51s
Regression Tests (hybrid_regression_AD.py)	3m 18s
Thread Sanitizer Tests (hybrid_regression.py)	27m 11s
Thread Sanitizer Tests (hybrid_regression_AD.py)	11m 7s
Address Sanitizer Tests (serial_regression.py)	14m 42s
Address Sanitizer Tests (serial_regression_AD.py)	6m 1s
	5h 33m 34s

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