tests: speed up fetchTextTest

tests: speed up fetchTextTest

The test is adding/resetting database data on every tests, however it is
not necessary.

Switch from addDBData to addDBDataOnce.
Drop the tablesUsed[] additions, they are not needed and trigger a
resetDB().
Change the textId### variables tracking created revisions to static
variables so they are kept between tests.

On my setup the test run time goes down from 1.7 sec to 0.5 sec.

Change-Id: Ibd3183b7fbf7dcf2c0c6d1268e1b94b11919cbf3