Add option to disable 077 umask (create new files with system default umask)

The option is only effective for either wallet-less builds or if
-disablewallet is specified as well.

Rebased-By: Wladimir J. van der Laan <laanwj@gmail.com>
Rebased-From: 34d5fc0 4e1a196 bd4307b d53a33b 7e09b36
Github-Pull: #4286