ensure selected cracker is available and viable

[jmartin-tech]

When no password cracker is installed cracker_version returns nil.
Guard against nil in the version check and consolidate detection of
a viable environment and application as a responsibility of the factory
that provides the instance.

Verification

List the steps needed to make sure this thing works

• Start msfconsole on a system without john or hashcat installed and a empty database available
• db_disconnect
• use crack_linux (or any other auxiliary/analyze/crack_* module)
• run
• Verify Failure is reported with database requirement noted.
• Start msfconsole on a system without john or hashcat installed
• db_connect
• use crack_linux
• run
• Verify Failure is reported noting no binary found.
• install john without jumbo patch
• use crack_linux
• run
• Verify Failure is reported noting jumbo patch is required.
• install john with jumbo patch
• use crack_linux
• run
• Verify Result reports no credentials cracked since none exist in the database.
• use crack_linux
• set action hashcat
• run
• Verify Failure is reported noting no binary found.
• install hashcat
• use crack_linux
• set action hashcat
• run
• Verify Result reports no credentials cracked since none exist in the database.

[h00die]

untested, but that does clean the code up!

[adfoster-r7]

Everything looks good to me; Just want to confirm that open question then I can land this 👍

[adfoster-r7]

Release Notes

Improved error message feedback when using the auxiliary/analyze/crack_* modules. Examples include notifying the user that the database needs to be active and having JohnTheRipper Jumbo patch installed.