Added fall back to "webrsync" in case of failure of "rsync" Portage synchronization. Added support for GPG signed Portage snapshot ("webrsync-gpg" feature).
"emerge-delta-webrsync" is also supported and preferred.
This code require #5198
Merge remote-tracking branch 'upstream/develop' into gentoo-webrsync

Conflicts:
	salt/modules/eix.py
Merge pull request #5212 from faust/gentoo-webrsync

Added fall back to "webrsync" in case of failure of "rsync" Portage synchronization and GPG support.