Update/samtools (#3595)

* Update samtools family to 1.4

* simple cleanup

* Make bzip depends_on for future versions too

var/spack/repos/builtin/packages/htslib/package.py

@@ -31,6 +31,8 @@ class Htslib(AutotoolsPackage):
     homepage = "https://github.com/samtools/htslib"
     url      = "https://github.com/samtools/htslib/releases/download/1.3.1/htslib-1.3.1.tar.bz2"
 
+    version('1.4', '2a22ff382654c033c40e4ec3ea880050')
     version('1.3.1', '16d78f90b72f29971b042e8da8be6843')
 
     depends_on('zlib')
+    depends_on('bzip2', when="@1.4:")