Fix OPENDJ-18 - keystore import failes due to empty PIN
Review CR-2353

* Removed constraints on the mandatory presence of a PIN, to allow use of empty PIN. 
   These contraints were implemented in several places :
  - configuration files : FileBasedKeyManagerProviderConfiguration.xml, PKCS11KeyManagerProviderConfiguration.xml
  - corresponding provider classes : FileBasedKeyManagerProvider.java, PKCS11KeyManagerProvider.java
  - setup tool : CertificateManager.java, InstallDS.java (for CLI), SecurityOptionsDialog.java (for GUI) 

* Removed corresponding admin messages that are no more used in FileBasedKeyManagerProviderCfgDefn.properties and PKCS11KeyManagerProviderCfgDefn.properties
* Removed corresponding messages that are no more used in extension.properties and quicksetup.properties
* Added management of issue JDK-6879539 that prevents usage of empty PIN. This issue occurs on JDK older than JDK7.
* Modified unit tests according to new behavior : FileBasedKeyManagerProviderTestCase.java, CertificateManagerTestCase.java

* Added a new utility method StaticUtils#stackTraceContainsCause to check if an exception contains a given cause.