kola/tests/ignition: add tests for ext4
kola/tests/ignition: add tests for ext4

Add tests for creating ext4 filesystems in ignition. Test both creating
a new ext4 filesystem in ignition and tests not overwriting an existing
filesystem.

dm0-/mantle,glevand/coreos--mantle,quantum/coreos-mantle,glevand/coreos--mantle,marineam/mantle,dm0-/mantle,marineam/mantle,quantum/coreos-mantle