Allow get_netrc_auth to raise parse/permission errors to caller
Allow get_netrc_auth to raise parse/permission errors to caller

If the netrc file exists but cannot be parsed or read, get_netrc_auth
silently fails.

Add a new argument `ignore_errors` which when set to False will cause
any parse/permission errors to be raised to the caller.  The default
value is True, which means the default behavior is unchanged.

Fixes #2654

Change-Id: I7436aaaf593178673ab84fd9e7ab4bcb0e3fe75e

psf/requests