seboolean: make it work with disabled SELinux

Sometimes it's necessary to configure SELinux before it's enabled on the
system. There's `ignore_selinux_state` which should allow it. Before
this change `seboolean` module failed on SELinux disabled system even
with `ignore_selinux_state: true` and SELinux policy installed while
`semanage boolean` worked as expected:

    $ ansible -i 192.168.121.153, -m seboolean -a "name=ssh_sysadm_login state=on ignore_selinux_state=true" all
    192.168.121.153 | FAILED! => {
        "ansible_facts": {
            "discovered_interpreter_python": "/usr/bin/python3"
        },
        "changed": false,
        "msg": "Failed to get list of boolean names"
    }

    $ ssh root@192.168.121.153 semanage boolean -l | grep ssh_sysadm_login
    ssh_sysadm_login               (off  ,  off)  Allow ssh to sysadm login

It's caused by `selinux.security_get_boolean_names()` and
`selinux.security_get_boolean_active(name)` which required SELinux
enabled system.

This change adds a fallback to semanage API which works in SELinux
disabled system when SELinux targeted policy is installed:

    ANSIBLE_LIBRARY=plugins/modules ansible -i 192.168.121.153, -m seboolean -a "name=ssh_sysadm_login state=on persistent=true ignore_selinux_state=true" all
    192.168.121.153 | CHANGED => {
        "ansible_facts": {
            "discovered_interpreter_python": "/usr/bin/python3"
        },
        "changed": true,
        "name": "ssh_sysadm_login",
        "persistent": true,
        "state": true
    }

    $ ssh root@192.168.121.153 semanage boolean -l | grep ssh_sysadm_login
    ssh_sysadm_login               (on   ,   on)  Allow ssh to sysadm login

Note that without `persistent=true` this module is effectively NO-OP now.

Signed-off-by: Petr Lautrbach <lautrbach@redhat.com>

plugins/modules/seboolean.py

@@ -81,23 +81,6 @@ def get_runtime_status(ignore_selinux_state=False):
     return True if ignore_selinux_state is True else selinux.is_selinux_enabled()
 
 
-def has_boolean_value(module, name):
-    bools = []
-    try:
-        rc, bools = selinux.security_get_boolean_names()
-    except OSError:
-        module.fail_json(msg="Failed to get list of boolean names")
-    # work around for selinux who changed its API, see
-    # https://github.com/ansible/ansible/issues/25651
-    if len(bools) > 0:
-        if isinstance(bools[0], binary_type):
-            name = to_bytes(name)
-    if name in bools:
-        return True
-    else:
-        return False
-
-
 def get_boolean_value(module, name):
     state = 0
     try:
@@ -173,7 +156,10 @@ def semanage_set_boolean_value(module, handle, name, value):
         semanage.semanage_handle_destroy(handle)
         module.fail_json(msg="Failed to modify boolean key with semanage")
 
-    if semanage.semanage_bool_set_active(handle, boolkey, sebool) < 0:
+    if (
+            selinux.is_selinux_enabled()
+            and semanage.semanage_bool_set_active(handle, boolkey, sebool) < 0
+    ):
         semanage.semanage_handle_destroy(handle)
         module.fail_json(msg="Failed to set boolean key active with semanage")
 
@@ -308,12 +294,9 @@ def main():
         # Feature only available in selinux library since 2012.
         name = selinux.selinux_boolean_sub(name)
 
-    if not has_boolean_value(module, name):
-        module.fail_json(msg="SELinux boolean %s does not exist." % name)
-
     if persistent:
         changed = semanage_boolean_value(module, name, state)
-    else:
+    elif selinux.is_selinux_enabled():
         cur_value = get_boolean_value(module, name)
         if cur_value != state:
             changed = True