The mysql config file is using INI format so use the iniset function to
manipulate it. This change also rearranges the config updates a bit
allowing us to make mulitple changes in a single sudo call. This reduces
the number of required process forks, and the number of times the 'functions'
file needs to be sourced a bit.
The "log-slow-queries" option is deprecated since mysql 5.1.29 and got
removed with 5.6.x. Use the newer slow-query-log-file/slow-query-log
settings instead. They are available since 5.1.12. This fixes a problem
with running devstack with mysql-5.6, which is e.g. part of openSUSE
13.1.
Change-Id: Iea28bf05c664b5387d51dae1a63a780344623596