Add cache locking functions in trylock variant

- Add cache trylock and read trylock functions.
- Introduce new error code -OCF_ERR_NO_LOCK.
- Change trylock functions in env to return this code in case of
  lock contention.

[ENV CHANGES REQUIRED]
Following functions should return 0 on success or -OCF_ERR_NO_LOCK
in case of lock contention:
- env_mutex_trylock()
- env_rwsem_up_read_trylock()
- env_rwsem_up_write_trylock()

Signed-off-by: Robert Baldyga <robert.baldyga@intel.com>

src/metadata/metadata.h

@@ -48,7 +48,7 @@ static inline void ocf_metadata_unlock(struct ocf_cache *cache, int rw)
 
 static inline int ocf_metadata_try_lock(struct ocf_cache *cache, int rw)
 {
-	int result = -1;
+	int result = 0;
 
 	if (rw == OCF_METADATA_WR) {
 		result = env_rwsem_down_write_trylock(
@@ -60,7 +60,7 @@ static inline int ocf_metadata_try_lock(struct ocf_cache *cache, int rw)
 		ENV_BUG();
 	}
 
-	if (!result)
+	if (result)
 		return -1;
 
 	return 0;