Improve JIRA integration by consolidating the findAllPrincipalNames() call with the individual calls to retrieve users.

JIRA calls findAllPrincipalNames(), then iterates over each username, asking for the user object.

Since findAllPrincipalNames() is implemented as a call to searchPrincipals() which fetches all the user details, we should optimise this code path by adding replacing the code that performs this in the crowd-integration-client with a call to searchPrincipals().

This will make life much better for LDAP (particularly AD), and custom directory users.