Add shell variables instead of ID values

Updates "Setting up tenants, users, and roles - manually"
section of the keystone install guide with shell variables
for each of the IDs referenced.
Fixed formatting by adding <screen><prompt>$</prompt> around <userinput>
Formatting: Replaced \t with whitespace, changed <literal> id Value
</literal> to <literal>id</literal> value, changed users to user's.

Change-Id: I4385d322a7b739cf78bc420c5617e69c01eb2810
Closes-Bug: #1073383
Merge "Add shell variables instead of ID values"