Bug fixes and minor changes to support new platforms

Pulled in the below pull requests:

#60
#59
#58

Bug fix and new provider support.

Fixed issues

• Issue #17 Add support for OCX device.
• Issue #20 "under development" error is thrown while importing the interface_create recipe from the
  Chef-Server.
• Issue #22 "netdev_vlan" resource action delete is not working fine while invoking from the JUNOS Chef-Client.
• Issue #23 RPC command error: commit-configuration is getting thrown on Invoking the "netdev_lag" resource from
  JUNOS Chef Client.
• Issue #27 Duplicate declaration of lag configuration in a recipe is giving NoMethodError: undefined method
  `properties' for nil:NilClass.
• Issue #30 Error in rerunning netdev_lag interface.
• Issue #33 undefined method `properties' for nil:NilClass error is thrown if the backup RE is unreachable.
• Issue #35 Error in running chef client from Backup RE.
• Issue #39 Getting 'Junos::Ez::NoProviderError' error on qfx device.
• Issue #42 Raise exception to handle warnings in .

Enhancement

• Add support for configuring l2_interface on MX device.
• Add support for provider 'group' for configuring JUNOS groups.