Added mysql in sql_connection line

In section 3, subsection a, it was mentioned
as "sql_connection=trove:TROVE_DBPASS@controller/trove"
but the actual line should be
"sql_connection=mysql://trove:TROVE_DBPASS@controller/trove"
Added word mysql which was not present earlier

Change-Id: I6d1e590e9046aacffb40ffaf2a1d952885412617
Closes-Bug: #1326119