{AH} add travis_retry for samtools/htslib/bcftools install
{AH} add travis_retry for samtools/htslib/bcftools install

kyleabeauchamp/pysam,TyberiusPrime/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,bioinformed/pysam,bioinformed/pysam,bioinformed/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,bioinformed/pysam,TyberiusPrime/pysam,TyberiusPrime/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,TyberiusPrime/pysam,bioinformed/pysam,TyberiusPrime/pysam,pysam-developers/pysam