Reformat code with google-java-format 1.7

The newer Gerrit branches are following the google-java-format 1.7 rules
for code formatting by now. The websession-flatfile plugin was not yet
adhering to these rules.

This change applies the format changes done by the google-java-format
1.7 tool.

Change-Id: I9e7e6ba9614431bb101fdd743fb8858a2df2b362