use bootstrap.php of core acceptance tests

[paurakhsharma]

Description

use the bootstrap.php from core

Related Issue

https://github.com/owncloud/QA/issues/605

Motivation and Context

Run accepectance tests through make command. e.g: make test-acceptance-api BEHAT_FEATURE=tests/acceptance/features/apiTestingApp/testing.feature:4 TESTING_REMOTE_SYSTEM=true NORERUN=true TEST_SERVER_URL=http://172.17.0.1/owncloud-core

How Has This Been Tested?

:robot:

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.