ARGUS-97: updated error handling in audit framework, with the following
changes:
 - Handle errors during audit framework initialization due to failure in
retrieving db password from the credential store
 - HDFS file logger initialization error due to missing configuration in
xasecure-audit.xml 
 - Introduced 'db retry min interval' configuration to control the wait
time before attempting to connect to the database after a failure
 - DbAuditProvider updated to handle exceptions while saving to DB,
instead of propagating to the caller; the provider also prints a warning
log, in log4j, with details of the audit event that failed to make to DB
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-argus
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/incubator-argus