Add MetaPhlAn2 dependency from Bio python module

MetaPhlAn2 additional script "read_fastx.py" can't work without Bio python module. If a python without installed Bio module is set, "MetaPhlAn2 classification" task launches and fails with incorrect error.

Stderr output:

Warning! Biom python library not detected!
Exporting to biom format will not work!
Traceback (most recent call last):
File "/Applications/U-1.32.0-full-rc2.app/Contents/MacOS/tools/metaphlan2-2.7.7/utils/read_fastx.py", line 9, in 
from Bio import SeqIO
ImportError: No module named Bio
OSError: fatal error running '/Applications/U-1.32.0-full-rc2.app/Contents/MacOS/tools/metaphlan2-2.7.7/utils/read_fastx.py'. Is it in the system path?

The following should be fixed:

1. Log parser should catch message

   ImportError: No module named Bio
   

   and generate an error message based on this information.

2. MetaPhlAn2 external tool should have a dependency from Bio python module.