XPath exists() method no longer applies (Camel 2.18)

[jkorab]

javax.xml.transform.TransformerException: Could not find function: exists

Updated tests in camel-cookbook-security. Check recipes if edits needed.

camel-cookbook-security/src/test/java/org/camelcookbook/security/xmlsecurity/SecurityAsymNamespacesSpringTest.java
camel-cookbook-security/src/test/java/org/camelcookbook/security/xmlsecurity/SecurityAsymNamespacesTest.java
camel-cookbook-security/src/test/java/org/camelcookbook/security/xmlsecurity/SecurityAsymSpringTest.java
camel-cookbook-security/src/test/java/org/camelcookbook/security/xmlsecurity/SecurityAsymTest.java
camel-cookbook-security/src/test/java/org/camelcookbook/security/xmlsecurity/SecuritySpringTest.java
camel-cookbook-security/src/test/java/org/camelcookbook/security/xmlsecurity/SecurityTest.java