Correct filesystem realm identity commands

The implementation of the filesystem realm DMR has changed, and the commands previously documented for creating and manipulating identities are now wrong.

See https://issues.jboss.org/browse/JBEAP-7167?focusedCommentId=13440016&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13440016 for an explanation.

The commands in 'Setup Caching for Security Realms' are fixed in JBEAP-7167, but there are similar commands for manipulating identities in the following sections that need to be corrected as well:

• Identity Management Guide: 'Configure Authentication with a Filesystem-Based Identity Store' https://doc-stage.usersys.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.1.beta/html-single/how_to_configure_identity_management/#elytron_apps_filesystemAuth
• SSO with Kerberos: '3.1. Adding a FORM Login as a Fallback' https://doc-stage.usersys.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.1.beta/html-single/how_to_set_up_sso_with_kerberos/#update_the_elytron_subsystem
• SSO with Kerberos: '2.4. Configuring the JBoss EAP Instance' https://doc-stage.usersys.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.1.beta/html-single/how_to_set_up_sso_with_kerberos/#elytron_http_auth_app