Ensure hiera step value is an integer

Ensure hiera step value is an integer

The step is typically set with the hieradata setting an integer value:

  {"step": 1}

However it would be useful for the value to be a string so that
substitutions are possible, for example:

  {"step": "%{::step}"}

This change ensures the step parameter defaults to an integer by
calling Integer(hiera('step'))

This change was made by manually removing the undef defaults from
fluentd.pp, uchiwa.pp, and sensu.pp then bulk updating with:

    find ./ -type f -print0 |xargs -0 sed -i "s/= hiera('step')/= Integer(hiera('step'))/"

Change-Id: I8a47ca53a7dea8391103abcb8960a97036a6f5b3