lisa.wlgen.fio: Introduce Fio as Workload

Fio is a highly-configurable I/O tester used by the block layer for testing
and as a general benchmark tool for storage. Even for scheduler investigations
Fio is interesting as in_iowait-setting tasks are treated differently.
To be able to create tests for them we introduce a simplistic lisa frontend.

Fio Workloads can now be created like:

ftest = Fio(target, filename="/dev/nvme0n1", name="test", rw="randread", runtime=50, bs='4k')
and then ran like any other:

with ftest:
    result = fiotestmmc.run()
    print(result.read_iops)

Signed-off-by: Christian Loehle <christian.loehle@arm.com>