docker/vttestserver: Add MYSQL_BIND_HOST env

[mcronce]

Description

Adds an optional MYSQL_BIND_HOST environment variable to the vttestserver container; if included, this is passed as -mysql_bind_host to vttestserver

Related Issue(s)

• docker image for vttestserver #7203
• docker images for vttestserver #7262

Checklist

• Should this PR be backported?
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

Run as follows:

$ docker run --rm -d -p33577:33577 -e PORT=33574 -e KEYSPACES=test -e NUM_SHARDS=1 -e MYSQL_BIND_HOST=0.0.0.0 vitess/vttestserver:mysql57
2c04c50156bd9ad7cac4b3f41bb653de37b78a0505c4154f1491e8d2730f5336
$ mysql -h127.0.0.1 -p33577
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.7.9-Vitess MySQL Community Server (GPL)

Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SHOW DATABASES;
+----------+
| Database |
+----------+
| test     |
+----------+
1 row in set (0.00 sec)

Impacted Areas in Vitess

Components that this PR will affect:

• Query Serving
• VReplication
• Cluster Management
• Build
• VTAdmin

[deepthi]

LGTM but DCO needs to be fixed before we can merge.

[mcronce]

@deepthi should be all set, thanks!