Previously, CommonsLoggingLiquibaseLogger referred to its
configured level and the underlying Commons Logging log when
determining if logging was enabled for a particular level. This did
not work as intended as setLogLevel was never called leaving the
configured level stuck at its default value of INFO. As a result of
this any logging at levels below INFO would not be output,
irrespective of the configuration of the underlying logging framework.

This commit updates CommonsLoggingLiquibaseLogger to rely purely on
the Commons Logging log when determining whether or not logging for
a particular level is enabled. This brings the implementation into
line with liquibase-slf4j [1] which provides similar functionality,
albeit using SLF4J rather than Commons Logging

Closes gh-2916

[1] https://github.com/mattbertolini/liquibase-slf4j/blob/master/src/main/java/liquibase/ext/logging/slf4j/Slf4jLogger.java