Enable Backblaze B2 backups

This reverts commit b1d703a5e7 and adds python3-setuptools per the first version of #1899 which fixes an installation error for the b2sdk Python package.

CHANGELOG.md

@@ -1,6 +1,13 @@
 CHANGELOG
 =========
 
+In Development
+--------------
+
+Control panel:
+
+* Backblaze B2 is now a supported backup protocol.
+
 v0.52 (January 31, 2021)
 ------------------------
 

management/templates/system-backup.html

@@ -18,6 +18,7 @@
         <option value="local">{{hostname}}</option>
         <option value="rsync">rsync</option>
         <option value="s3">Amazon S3</option>
+        <option value="b2">Backblaze B2</option>
       </select>
     </div>
   </div>

setup/management.sh

@@ -27,9 +27,10 @@ done
 # provision free TLS certificates.
 apt_install duplicity python-pip virtualenv certbot
 
+# b2sdk is used for backblaze backups.
 # boto is used for amazon aws backups.
 # Both are installed outside the pipenv, so they can be used by duplicity
-hide_output pip3 install --upgrade boto
+hide_output pip3 install --upgrade b2sdk boto
 
 # Create a virtualenv for the installation of Python 3 packages
 # used by the management daemon.
@@ -50,7 +51,7 @@ hide_output $venv/bin/pip install --upgrade \
 	rtyaml "email_validator>=1.0.0" "exclusiveprocess" \
 	flask dnspython python-dateutil \
   qrcode[pil] pyotp \
-	"idna>=2.0.0" "cryptography==2.2.2" boto psutil postfix-mta-sts-resolver
+	"idna>=2.0.0" "cryptography==2.2.2" boto psutil postfix-mta-sts-resolver b2sdk
 
 # CONFIGURATION
 

setup/system.sh

@@ -131,7 +131,7 @@ apt_get_quiet autoremove
 # * openssh-client: provides ssh-keygen
 
 echo Installing system packages...
-apt_install python3 python3-dev python3-pip \
+apt_install python3 python3-dev python3-pip python3-setuptools \
 	netcat-openbsd wget curl git sudo coreutils bc \
 	haveged pollinate openssh-client unzip \
 	unattended-upgrades cron ntp fail2ban rsyslog