Prevent concurrent write opens/migrations

[yhr]

Adresses #195

[metaspace]

In file included from plugin/zenfs/fs/io_zenfs.cc:11:
plugin/zenfs/fs/io_zenfs.cc: In constructor 'rocksdb::ZonedWritableFile::ZonedWritableFile(rocksdb::ZonedBlockDevice*, bool, std::shared_ptr<rocksdb::ZoneFile>)':
plugin/zenfs/fs/io_zenfs.cc:769:20: error: 'using element_type = class rocksdb::ZoneFile' {aka 'class rocksdb::ZoneFile'} has no member named 'IsOpenForWrite'; did you mean 'IsOpenForWR'?
  769 |   assert(zoneFile->IsOpenForWrite());
      |                    ^~~~~~~~~~~~~~

[metaspace]

AquireWRLock() -> AcquireWRLock(), same for Try..

[yhr]

AquireWRLock() -> AcquireWRLock(), same for Try..

doh! fixed!