Fix language tests- disable exit phase

Plugin now clears language during task exit, so phase must be disabled
for tests.
Disable retry_failed in test_invalid_urls

Retry_failed rejecting failed entries was causing tests to fail as
entries would be flagged as rejected rather than failed.
Fix TestBatotoRewriter.test_garbage_series

Enables url rewriter and disables retry_failed.
Update test_get_chapter_pages to new functionality

Tests changed to match how plugin now functions (not making per-page
entries, etc).
Fix typo in string_to_time which could cause abort
BeautifulSoup 4 compatibility tweak
Set identified_by during series modification

If no id regexps are present and identified_by is not set, plugin will
set identified_by to 'sequence', ensuring provided sequence_regexp is
used.
Improve reliability of test_chapter_match_parser

Now ensures the pack identifier is exactly what's desired, previously
could pass by luck.