Added dbname, host, username etc explicitly
Added an example for linear regression input test

Summary:

* LinregrOutputTestCase:
  - Answer file is a single file containing all R results
  - Result file name contains corresponding parameter values
  - Answers are created by external program (here we use R)

* LinregrInputTestCase
  - Multiple answer files, each of which is for one test case
  - Result & answer file names do not have parameter values, but instead
  use an integer to index the files
  - Answers are created by a run of the test itself. And the output is
  used as the baseline for future tests.
Minor changes
Added data loader and README files for each folder
skipping tests is enabled

Also one can choose not to create test case files if they are already
there
MInor changes
Make the MADlibTestCase easy to use

* Move db_settings, incr, _create_ans, _create_case all into
  MADlibTestCase

* _create_ans, _create_case are controlled by environment variables
Drastically change directory structure, database configuration can be
chosen from dbsettings by user through an environment variable
Use the recommended way to skip test and created tests

* Input tests are working now

* To do output tests
Skip can be controlled by SKIP
Fixed a small bug
Move schema_madlib and schema_testing into higher level

Put them into dbsettings.py

Also clean up madlib_test.py

Copy the old MADmark datasets folder to here
Make a differece between root user and testing user

Running the tests only need a normal user

But loading data might need a root user
Adjust the directory structure again
Data loader working now
Added a connector function to R

Also allow SKIP to use skip file in current path