testsuite: Introduce -X option for running on big-endian systems #342

Job	Run time
Build Netatalk testsuite container	1m 3s
Build Netatalk container	48s
Netatalk container dry run	6s
AFP login test - AFP 2.1	6s
AFP spec test (Readonly) - AFP 2.1	6s
AFP login test - AFP 3.4	7s
AFP spec test (Readonly) - AFP 3.4	6s
AFP spec test - AFP 2.1	56s
AFP spec test - AFP 2.2	56s
AFP spec test - AFP 3.0	1m 5s
AFP spec test - AFP 3.1	1m 5s
AFP spec test - AFP 3.2	1m 7s
AFP spec test - AFP 3.3	1m 7s
AFP spec test - AFP 3.4	1m 4s
	9m 42s

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