Switch import testing order for Bio.Cluster test
Clean up test files after running BWA & samtools tests
Put return code at start of Bio.Application error message.

This is in case the ApplicationError exception message
gets truncated and this information is lost (e.g. due to
a very long command line from several long file names).
Just use relative paths in this test
Update due to changed Bio.Application error message
Match case; I should install this dependency locally...