core: Removing leftover of rootPassword

On host install action (or reinstall) we validated that
rootPassword parameter is passed. This validation is a leftover of
previous implementation. Currently all parameters in reinstall action are
optional.

Change-Id: I675b349313c422d13a8f46f8d3aa1eca456ee90a
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1029050
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>