HTSLIB env variable is required but not checked

[jrandall]

The FileType class builds a path to the htsfile command by assuming that the HTSLIB env variable is set, but nothing ever checks to make sure it is set (so it doesn't work even if htsfile s in the PATH):

vr-pipe/modules/VRPipe/FileType/hts.pm

Line 41 in 29343e9

my $htsfile_exe = file($ENV{HTSLIB}, 'bin', 'htsfile');

As a result, we end up getting a lot of "...exists but is the wrong type" messages from StepRole, when the real problem was just that HTSLIB is not set.

I would suggest that VRPipe::FileType::hts should check to make sure that HTSLIB env variable is set and throws an error if not.