Use a single method for generating log error messages and stack traces if needed

Motivation: OPENDJ-6528 and OPENDJ-6505.

We could do with rationalizing some of our exception logging. At the moment we have many methods that output different varieties of exception message:

• com.forgerock.opendj.util.StaticUtils#getExceptionMessage - this is the method used for the CME in this bug. It does not include any stack trace when the main exception has a message
• com.forgerock.opendj.util.StaticUtils#stackTraceToSingleLineString(java.lang.StringBuilder, java.lang.Throwable, boolean)
• com.forgerock.opendj.util.StaticUtils#stackTraceToSingleLineString(java.lang.Throwable, boolean) - delegates to method above
• org.opends.server.util.StaticUtils#getBacktrace
• org.opends.server.util.StaticUtils#getExceptionMessage - does some stuff then delegates to SDK equivalent
• org.opends.server.util.StaticUtils#stackTraceToSingleLineString - delegates to SDK
• org.opends.server.util.StaticUtils#stackTraceToString(java.lang.Throwable) - no delegation

I wonder if we could replace all these with a single method that combines getExceptionMessage(), which handles recognized exception types, then fall through to stackTraceToSingleLineString() with full stack always set to true for unrecognized exceptions.

Additional input from Jean-Noël Rouvignac: I see a lot of code calling e.getMessage() or e.getLocalizedMessage() (Java exceptions) or e.getMessageObject() (OpenDJ exceptions). I would ban them all in favour of a single call to StaticUtils.getExceptionMessage(e) which does the right thing (TM).