make format paramter optional to cu.load function when config passed as a string
removed warning messages
reverting changes done for removing PendingDeprecationWarning, as it breaking in py 2.6
changed test cases to check set key, added 2 more test case to cover old code
pep8 corrections
Merge branch 'master' of https://github.com/juniper/py-junos-eznc into format-optional
Merge pull request #322 from vnitinv/format-optional

Format optional