rename {owner,group}_id params to {owner,group}
modernize Gemfile/Rakefile/spec_helper boilerplate
add certdir param to nssdb::create type

Defaults to the type's title.
change nssdb::add_cert type to treat it's title as the default nickname

Previously, the title was being used as the default cert param value.
update travis matrix
change nssdb::add_cert_and_key type to treat it's title as the default nickname

Previously, the title was being used as the default certdir param value.
rename password.conf to nss-password.txt

The password.conf name is rather generic and hard to associate with nss
files when the nss db is in a path with other configuration files.