Python sqlContext.getConf() add one argument version

[mathieulongtin]

What changes were proposed in this pull request?

In Python, sqlContext.getConf didn't allow getting the system default (getConf with one parameter).

Now the following are supported:

sqlContext.getConf(confName)  # System default if not locally set, this is new
sqlContext.getConf(confName, myDefault)  # myDefault if not locally set

I also added doctests to this function

How was this patch tested?

Manually, but doctests were added.

Cherrypick commit 16a74ac.

[AmplabJenkins]

Can one of the admins verify this patch?

[rxin]

Can you update the pull request title to include more information?

[rxin]

Also why do we need to introduce csv dependency?

[mathieulongtin]

Sorry, just cherry-pick the last commit on that branch. I'm new using git with large project that change all the time.

[mathieulongtin]

Nevermind, somehow picked the wrong branch entirely.