[Compaction] Default GetColumnFamilyMetaData() now returns Status::NotSupported().

Summary:
Default GetColumnFamilyMetaData() now returns Status::NotSupported().

Test Plan:
make
[Compaction] Ensure compensated_file_size >= size in SstFileMetaData.

Summary:
Ensure compensated_file_size will always greater than or equal to size
in SstFileMetaData.

Test Plan:
Add check in DatabaseMetaDataTest
[Compaction] Change functions of Compactor to be non-const.

Summary:
Change functions of Compactor to be non-const, giving classes which
implement Compactor the flexibility to update their local stats.

Test Plan:

Reviewers:

Subscribers:
[Compaction] Fix lint warnings.
[Compaction] Print info log when background compaction might not be properly set.

Summary:
Print info log when background compaction might not be properly set.
[Compaction] Compactor now takes a const pointer to Options.

Summary:
Compactor now takes a const pointer to Options.  This allows Compactor
to be customized via the usual rocksdb Options.

Test Plan:
make