Merge remote-tracking branch 'upstream/staging/electro-release' into staging/electro-release
Favor MSF_DATABASE_CONFIG for paths['config/database']

MSP-10848

Use these locations, in order for
Metasploit::Framework::Application.config.paths['config/database']:

1. MSF_DATABASE_CONFIG environment variable
2. ~/.msf4/database.yml (if it exists)
3. config/database.yml