FIPS and Self Signed Certs

This pull request contains two enhancements:

* It adds a new type for creating self signed cert and key directly in the NSS DB rather then using a preexisting key with add_cert_and_key

* It adds an option to the create type for enabling FIPS mode on the DB
Since nsstools does an include of nsstools::params and this type includes nsstools, it is not strictly required. I added it because of the change to line 70 where now the name of the password file is a parameter included in nsstools::params rather then having to keep track of the hard coded string "nss-password.txt" everywhere.

I thought it would be strange in create_cert_and_key.pp to hard code in 'new-password.txt', hence the move of that string to the params class. If you would rather have it refereed to has a hard coded string everywhere I could re-build the commit without that bit.