qemu-iotests: Support varargs syntax in FilePaths

qemu-iotests: Support varargs syntax in FilePaths

Accept variable number of names instead of a sequence:

    with FilePaths("a", "b", "c") as (a, b, c):

The disadvantage is that base_dir must be used as kwarg:

    with FilePaths("a", "b", base_dir=soc_dir) as (sock1, sock2):

But this is more clear and calling optional argument as positional
arguments is bad idea anyway.

Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200828232152.205833-4-nsoffer@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>