Fix scoping error that caused stack trace

MSP-11489

When cracking an NTLM hash with an existing Login,
Creation#create_cracked_credential would fail with:

  NameError undefined local variable or method `core'
Add specs for Creation#create_cracked_credential
Merge branch 'bug/MSP-11489/cracked-scope'

Conflicts:
	lib/metasploit/credential/creation.rb
Dropping PRERELEASE from version.rb