test_55:
Reformat Lustre filesystem each time, because pre-defined fsname
is 'lustre', and for seperate MDS and MGS, MGS won't be reformated,
trying to reformat a new filesysem with same fsname will make OST
and MDS fail to mount.
test_68:
Mount MGS in the end of test if MGS and MDS are seperated.
test_72:
Reformat MGS if MGS and MDS are seperated. Otherwise, there
will be conflicts.
test_75:
Reformat all devices otherwise 76a might fail.