suppress error log when postgre database does not exist

[javeme]

error log like this:

May 24, 2019 1:25:14 PM org.postgresql.Driver connect
SEVERE: Connection error:
org.postgresql.util.PSQLException: FATAL: database "hugegraph" does not exist

Change-Id: I48aebac67ec98f5c05b96239b497940150542dcc

[codecov]

Codecov Report

Merging #527 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #527      +/-   ##
============================================
+ Coverage     69.94%   69.98%   +0.04%     
- Complexity     3392     3395       +3     
============================================
  Files           216      216              
  Lines         16503    16506       +3     
  Branches       2359     2359              
============================================
+ Hits          11543    11552       +9     
+ Misses         3701     3695       -6     
  Partials       1259     1259

Impacted Files	Coverage Δ	Complexity Δ
...u/hugegraph/backend/store/mysql/MysqlSessions.java	69.93% <100%> (+0.18%)	17 <1> (+1)	⬆️
...h/backend/store/postgresql/PostgresqlSessions.java	65% <100%> (+3.88%)	5 <2> (+2)	⬆️
...va/com/baidu/hugegraph/backend/cache/RamCache.java	72.15% <0%> (-0.4%)	44% <0%> (-1%)
...du/hugegraph/backend/tx/GraphIndexTransaction.java	80% <0%> (+0.63%)	146% <0%> (+1%)	⬆️
...n/java/com/baidu/hugegraph/task/TaskScheduler.java	52.69% <0%> (+1.24%)	27% <0%> (+1%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9188fb2...4f7e18b. Read the comment docs.

[zhoney]

call it from PostgresqlSessions.createDatabase()