Allow custom user and port for builder host

When ssh options are set, they overwrite username and password passed as ssh builder uri. Passing part of uri for ssh-kit is fine, as it then properly extracts username and password and forwards it as host.ssh_options (in which case it's no longer empty)

test/fixtures/deploy_with_remote_builder_and_custom_ports.yml

@@ -0,0 +1,45 @@
+service: app
+image: dhh/app
+servers:
+  web:
+    - "1.1.1.1"
+    - "1.1.1.2"
+  workers:
+    - "1.1.1.3"
+    - "1.1.1.4"
+registry:
+  username: user
+  password: pw
+
+accessories:
+  mysql:
+    image: mysql:5.7
+    host: 1.1.1.3
+    port: 3306
+    env:
+      clear:
+        MYSQL_ROOT_HOST: '%'
+      secret:
+        - MYSQL_ROOT_PASSWORD
+    files:
+      - test/fixtures/files/my.cnf:/etc/mysql/my.cnf
+    directories:
+      - data:/var/lib/mysql
+  redis:
+    image: redis:latest
+    roles:
+      - web
+    port: 6379
+    directories:
+      - data:/data
+
+readiness_delay: 0
+
+ssh:
+  user: root
+  port: 22
+
+builder:
+  remote:
+    arch: amd64
+    host: ssh://app@1.1.1.5:2122