fix database download steps

[AldisiRana]

when the database file doesn't exist, bio2bel_drugbank asks the user to move the full database.xml to the .bio2bel/drugbank directory, but the code requires the zip file

• even though the code has an option to parse the xml file, the parser is not able to find the xml file because of the PATH variable

UPDATE: I've tried to populate using the zip file but the process gets eliminated after 1%

[cthoyt]

Too much memory consumption?

[cthoyt]

The newer file is definitely a lot bigger than before (like 1.4GB in release 5.1.4 vs .8GB in release 5.1.1)

[AldisiRana]

it doesn't actually say why it eliminates it. The process just stops after 1%.
I'm also using the old version (so the 0.8GB file), and it populated before so I don't know why it is not working now

[AldisiRana]

I've added a picture to clarify

[cthoyt]

Add some more logging to bio2bel_drugbank then... it's hard to say where it's getting stuck