Force datastore validation by option set

cmd_psh_payload relies on datastore options to have a proper
data type down the call chain. When modules are created with string
values for all data store options, a conditional naively checking
what should be a boolean value for false/nil? would return true
for a string representation of "false."

Ensure that datastore options are validated prior to using them
to set variables passed into Rex methods.

Author: RageLtMan

lib/msf/core/exploit/powershell.rb

@@ -188,6 +188,7 @@ def run_hidden_psh(ps_code, payload_arch, encoded)
   #
   # @return [String] Powershell command line with payload
   def cmd_psh_payload(pay, payload_arch, opts = {})
+    options.validate(datastore)    
     opts[:persist] ||= datastore['Powershell::persist']
     opts[:prepend_sleep] ||= datastore['Powershell::prepend_sleep']
     opts[:method] ||= datastore['Powershell::method']