Fix OFF logging threshold

[trask]

Resolves #2590

[jeanbisutti]

(suggestion) This method might be moved in AgentLogExporter and called around line 84. So all the log logic would be in the place where we need it. A boolean exportLog(LogData log, String configuredLogThreshold) method might then be added and contains all the log level logic for the export. The configuration object would then represent the log level as a string an not an int.

[trask]

this looks a bit more challenging, as we are also using this method for fail-fast validation of the configuration:

ApplicationInsights-Java/agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/configuration/Configuration.java

Lines 54 to 55 in 560c7d5

	public void validate() {
	instrumentation.logging.getSeverity();