Add support for crypted passwords to password lookup

Added new parameter 'encrypt' with same semantics from that of
vars_prompt. When encryption is requested a random salt will be
generated and stored along the password in the form:
'<password> salt=<salt>'.

Also store passwords with an ending '\n' for easier looking at files
with console tools. File content was being already rstripped so this
is harmless.

docsite/latest/rst/playbooks2.rst

@@ -537,6 +537,15 @@ This length can be changed by passing an extra parameter::
                     target=/tmp/{{ client }}_{{ tier }}_{{ role }}_backup.sql
           with_password: credentials/{{ client }}/{{ tier }}/{{ role }}/mysqlpassword length=15
 
+        (...)
+
+        # create an user with a given password
+        - user: name=guestuser
+                state=present
+                uid=5000
+                password={{ item }}
+          with_password: credentials/{{ hostname }}/userpassword encrypt=sha256_crypt
+
 Setting the Environment (and Working With Proxies)
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