def get_sample_name_from_vcf_file(infile):
header_lines =  get_header_lines_from_vcf_file(infile)<EOL>return get_sample_name_from_vcf_header_lines(header_lines)<EOL>
Assumes only one sample in the file.
    Raises error if badly formatted #CHROM line.
    Returns None if no #CHROM line found