PGLog: clear missing on backfill reset

When backfill is reset, the missing set should be cleared
since all objects are >last_backfill.

Fixes: #5320
Signed-off-by: Samuel Just <sam.just@inktank.com>
add clear_range, rmkeyrange plubming (but not implementation)
DBObjectMap: return 0 in clear_range

Signed-off-by: Samuel Just <sam.just@inktank.com>
FileStore,DBObjectMap: handle rmkeyrange in FileStore

Handling it in DBObjectMap really only has efficiency
advantages if the object is a clone.  For now, this
approach simplifies the testing of DBObjectMap.

Signed-off-by: Samuel Just <sam.just@inktank.com>
PG: remove ondisklog usages from PG

ondisklog is now only relevant for the divergent priors mapping.

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGLog: pass only divergent_priors, not ondisklog

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGLog: remove other ondisklog references

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGLog: remove OndiskLog

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd_types: move code for pg_log_entry_t::get_key_name into eversion_t

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGLog: track dirty_to and dirty_from for log

This allows the log to only write out/clear the keys
which have actually changed.

Signed-off-by: Samuel Just <sam.just@inktank.com>
PG: move instances of log dirtying in PG into PGLog

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGLog: replace dirty_log with mark_dirty_*

Signed-off-by: Samuel Just <sam.just@inktank.com>
PG,PGLog: remove dirty_log arguments

Signed-off-by: Samuel Just <sam.just@inktank.com>
test/osd/TestPGLog: fix pglog unittests for dirty_log and ondisklog

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGLog: touch log on first write_log

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGLog: improve debugging for write_log

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGLog: add debug check on written keys, verify on write

Signed-off-by: Samuel Just <sam.just@inktank.com>