More changes to library functions and testcase decorator

- Removed get_vol_types
- Added get_config_data to get all config related data
- Change the mount_volume to return 0, if already mounted
- Removed asserts
- decorator now calls test functions without any arguements

Signed-off-by: M S Vishwanath Bhat <vbhat@redhat.com>
Merge branch 'master' of github.com:msvbhat/glusterfs-automation-framework