Description of problem:
Request for reinstall action requires <root_password></root_password> as part of the request although we connect by public key 

--- the request
<action>                                                  
<root_password></root_password>   <-- without those
<ssh>                                                                          
<port>22</port>                                                                
<authentication_method>PublicKey</authentication_method>                        
</ssh>                                                                          
</action>
---

returns the failure from BZ 987982 (rootPassword is required)

How reproducible:
100%

Steps to Reproduce:
1. add host, put it on maintainace
1. run the above REST API action

Actual results:
Failing the operation on required field rootPassword 


Expected results:
Should work without any warning if pk is verified

Additional info:
we keep validate rootPassword field in BackendHostMapper-
 validateParameters(action, "rootPassword");

It shouldn't be there at all