Fixed the missing opening bracket and grammar

There is a closing bracket, but not the opening bracket, in the first sentence of logging module guide here,
http://docs.openstack.org/admin-guide-cloud/content/section_manage-logs.html
Also fixed minor grammatical mistake inserting 'is' .
Partial-Bug: #1251195

Change-Id: I29c7c2f186ec2abb248f6d199382d054769ca992
Merge "Fixed the missing opening bracket and grammar"