Issue #2502 #2586 was fixed.
Fixed issue #2582
Issue #2520 was fixed.
Merge remote-tracking branch 'origin/1.7.7' into 1.7.7
Fix #2581 Close WAL when DB is closing

(cherry picked from commit b1d207ffcaa77b25aa87aad744329f8b4c1a667a)

Conflicts:
	core/src/main/java/com/orientechnologies/orient/core/storage/impl/local/OAbstractPaginatedStorage.java
	core/src/main/java/com/orientechnologies/orient/core/storage/impl/local/paginated/wal/ODiskWriteAheadLog.java
Checked if compression is going to be changed in non empty cluster
WAL MT speed up.
Merge remote-tracking branch 'origin/1.7.7' into 1.7.7
Paginated cluster test was fixed.
Merge branch '1.7.7' into develop

Conflicts:
	commons/src/main/java/com/orientechnologies/common/io/OFileUtils.java
	core/src/main/java/com/orientechnologies/orient/core/config/OGlobalConfiguration.java
	core/src/main/java/com/orientechnologies/orient/core/storage/impl/local/paginated/OLocalPaginatedStorage.java
	core/src/main/java/com/orientechnologies/orient/core/storage/impl/local/paginated/OPaginatedCluster.java
	core/src/main/java/com/orientechnologies/orient/core/storage/impl/local/paginated/wal/OWriteAheadLog.java
	distributed/config/orientdb-dserver-config.xml
	distributed/src/test/resources/orientdb-dserver-config-0.xml
	distributed/src/test/resources/orientdb-dserver-config-1.xml
	distributed/src/test/resources/orientdb-dserver-config-2.xml
	distributed/src/test/resources/sharded-dserver-config-0.xml
	distributed/src/test/resources/sharded-dserver-config-1.xml
	distributed/src/test/resources/sharded-dserver-config-2.xml