Quote blastdbcmd -db arguments to allow multiple dbs

Some refactoring resulted in broken command, which was causing errors
when run against multiple databases. Fix this. See NCBI BLAST+ help
manual for reference.

Signed-off-by: Vivek Rai <vivekraiiitkgp@gmail.com>
Show database ids, not full path to database, if error retrieving sequences.

User / admin can get full path from `sequenceserver -l`.

Plus slight refactoring around sequence retrieval.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>