convert variantcaller specification to proper vardict command, handling
    string or list specification

def get_vardict_command(data):
    """
    convert variantcaller specification to proper vardict command, handling
    string or list specification
    """
    vcaller = dd.get_variantcaller(data)
    if isinstance(vcaller, list):
        vardict = [x for x in vcaller if "vardict" in x]
        if not vardict:
            return None
        vardict = vardict[0]
    elif not vcaller:
        return None
    else:
        vardict = vcaller
    vardict = "vardict-java" if not vardict.endswith("-perl") else "vardict"
    return vardict