keyfile argument distiguish managed and unmanaged mode

keyfile argument distiguish managed and unmanaged mode

Arguments --keyfile, -k for managed mode
and
--keyfile-ro, -K for unmanaged (readonly) mode.

Automatic setting based on the file permission is removed because it was
confusing and could easily lead to state where automatic update does not
happen because of unexpected file permissions.

Check if folder is writeable was moved into Lua code.

Default unmanaged keyfile path can be specified at compile
time with option KEYFILE_DEFAULT. This default
configuration can be disabled in configuration file with
trust_anchors.keyfile_default = nil.