remove SL4/SL5 PARTEDEXTRA code, fix on always using 'u MB'
use parted with 'u MB' also in other places
fix mock commands to use 'u MB' where appropriate
adjust all unittests with new PARTEDEXTRA set to 'u MB'
Merge pull request #21 from stdweird/remove_SL4_support

Remove SL4 support by fixing the parted units to use MB