Update for BLAST+ 2.2.27

This branch switches the tool dependency from BLAST+ 2.2.26 to BLAST+ 2.2.27, using this package on the Test Tool Shed: http://testtoolshed.g2.bx.psu.edu/view/iuc/package_blast_plus_2_2_27

I've not yet setup the matching IUC repository on the main Tool Shed. The package `tool_dependencies.xml` is being tracked within this repository (already on the master branch - and for BLAST+ 2.2.28 as well).

As an aside, I think I/we should automate regenerating the test output files to make this easier to do for the next BLAST version increment.

TravisCI looks good: https://travis-ci.org/peterjc/galaxy_blast/builds/12138489

Assuming no problems on the Test Tool Shed, I think this should be ready to push to the main Tool Shed along with Nicola's and Bjoern's enhancements.

CC @nsoranzo, @bgruening, @jmchilton, etc for comment/review.