Make origin of log message visible

[temeo]

Currently all messages are logged without any indication where they come from. As there will now be three different sources of wsrep logging in the application log (application patch, wsrep-lib, provider library), it may become difficult to locate the origin of the log message.

It was suggested to provide a prefix for all log messages which would indicate the origin:

• lib - originates from wsrep-lib
• provider library name - originates from loaded provider library

With this scheme, the log messages in the application log would look like following, assuming that the application logging callback uses WSREP prefix for all log messages corresponding to wsrep functionality:

WSREP: This message comes from the application wsrep patch
WSREP-lib: This message comes from wsrep-lib
WSREP-Galera: This message comes from loaded Galera provider library