Fix file permission issue in toxchat/bootstrap-node

/var/lib/tox-bootstrapd on the host is owned by hosts's tox-bootstrapd
and chowned 700, but the container attempts to access it as its own
tox-bootstrapd user with possibly different uid:gid, which will fail if
host's tox-bootstrapd user has different uid:gid than the tox-bootstrapd
user inside the container.

This change makes the container use host's tox-bootstrapd uid:gid, which
fixes the issue.

.travis/tox-bootstrapd-docker

@@ -14,6 +14,7 @@ sudo useradd \
   --user-group tox-bootstrapd
 sudo chmod 700 /var/lib/tox-bootstrapd
 docker run -d --name tox-bootstrapd \
+  --user "$(id -u tox-bootstrapd):$(id -g tox-bootstrapd)" \
   -v /var/lib/tox-bootstrapd/:/var/lib/tox-bootstrapd/ \
   --ulimit nofile=32768:32768 \
   -p 443:443 \

other/bootstrap_daemon/README.md

@@ -249,6 +249,7 @@ sudo useradd \
 sudo chmod 700 /var/lib/tox-bootstrapd
 
 docker run -d --name tox-bootstrapd --restart always \
+  --user "$(id -u tox-bootstrapd):$(id -g tox-bootstrapd)" \
   -v /var/lib/tox-bootstrapd/:/var/lib/tox-bootstrapd/ \
   --ulimit nofile=32768:32768 \
   -p 443:443 \
@@ -284,7 +285,9 @@ Then rebuild and run the image again:
 ```sh
 tar c $(git ls-files) | docker build -f other/bootstrap_daemon/docker/Dockerfile -t toxchat/bootstrap-node -
 docker run -d --name tox-bootstrapd --restart always \
+  --user "$(id -u tox-bootstrapd):$(id -g tox-bootstrapd)" \
   -v /var/lib/tox-bootstrapd/:/var/lib/tox-bootstrapd/ \
+  --ulimit nofile=32768:32768 \
   -p 443:443 \
   -p 3389:3389 \
   -p 33445:33445 \