tests: journal, added 10x rollover, random item size
journal: correct file end position detection

This fixes an issue where the journal file could grow over the set
limit if:
1. Last entry on previous rollover did not fill the file fully
2. The information about the difference between the last entry and the
file size is lost

In such case, the end of file is detected later, leading to
increase of the file size by the size of the first evicted entries.
Merge branch 'journal_file_end_check' into 'master'

Correct detection of journal end position.

MR !316