Split worker database configuration

Qserv configuration tool now configures
worker database apart from master database.
Previous code was creating both czar and
worker databases on both czar and worker
MySQL instances.
Factorize SQL loader for czar/worker configurations

Qserv czar and worker configurations are now distinct
procedures, but they use the same script to load
sql files related to czar and worker databases.
Sharpen SQL scripts for worker and czar configuration

SQL scripts launched by configuration tool for czar
and worker now create the right tables at the
right place, with more accurate permissions.
Fix MySQL sock path computation in configuration

Qserv configuration tool no more overide MySQL sock path
while reading meta-configuration file.
Change log level for xrootd to MySQL connection error

Qserv plugin for xroot now print an ERROR message
when MySQL connection fails.
Improve configuration tool code

- removal of one *.swp file from git
- lazy formatting for one logger message
- STEP_DOC dict is more explicit
- use of list comprehension instead of map
- improve shell scripts robustness to variables
  with whitespaces
- use sh instead of bash when possible
- fix fatal error message
Merge branch 'u/fjammes/DM-1446'