library: Fix new-style modules check mode

Running the `ceph_crush.py`, `ceph_key.py` or `ceph_volume.py` modules in check
mode resulted in the following error:

```
New-style module did not handle its own exit
```

This was due to the fact that they simply returned a `dict` in that case,
instead of calling `module.exit_json()`.

Signed-off-by: Benoît Knecht <bknecht@protonmail.ch>
(cherry picked from commit 85dd405814)

library/ceph_crush.py

@@ -166,14 +166,14 @@ def run_module():
         changed=False,
         stdout='',
         stderr='',
-        rc='',
+        rc=0,
         start='',
         end='',
         delta='',
     )
 
     if module.check_mode:
-        return result
+        module.exit_json(**result)
 
     startd = datetime.datetime.now()
 

library/ceph_key.py

@@ -530,14 +530,15 @@ def run_module():
         changed=changed,
         stdout='',
         stderr='',
-        rc='',
+        rc=0,
         start='',
         end='',
         delta='',
     )
 
     if module.check_mode:
-        return result
+        module.exit_json(**result)
+
     startd = datetime.datetime.now()
 
     # will return either the image name or None

library/ceph_volume.py

@@ -566,14 +566,14 @@ def run_module():
         changed=False,
         stdout='',
         stderr='',
-        rc='',
+        rc=0,
         start='',
         end='',
         delta='',
     )
 
     if module.check_mode:
-        return result
+        module.exit_json(**result)
 
     # start execution
     startd = datetime.datetime.now()