Fix configure db script

[dgenezini]

The configure.db file is referenced in the Docker Hub documentation but does not work.

Fixes:

• Variable i was being concatenated instead of incremented, making the script not wait for SQL Server to boot;
• Ignoring errors from the select SUM(state) from sys.databases command;
• Changed SA_PASSWORD variable to MSSQL_SA_PASSWORD (The correct one);
• Removed chmod from Dockerfile.

Improvements:

• Configurable number of retries;
• Explicit unit of time (seconds) on the sleep command;

[dgenezini]

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[esdrasbeleza]

I had exactly the same issues and this PR fixed them!