Support Drush 9

Problem/Motivation

As per drush documentation, Drush 9 should be used for Drupal core >= 8.4.x. Considering we have stable core version 8.6.x and avoid composer depenedecy issues (as new modules require drush 9), we have to port Drush commands to version 9

Proposed resolution

Since Drush 8 commands are not compatible with Drush 9, we have to port them. This Blog post has few automated steps to start with.

Remaining tasks

1. Port
2. Test
3. Review

User interface changes

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

Support Drush 9