bitbucket/resource_plugin: Install plugins with URI
Existing approach based on PostFileUpload() doesn't seem to work for Bitbucket server 6.10.
Replace it with InstallPluginWithUri().
* Changed the error checking when importing an existing group for bitbucket so that the duplicate group error is not thrown
* Added two acceptance tests
* Updated the ReadMe.md with accurate instructions since the previous ones were not working for us
* Updated the Makefile to set the maximum number of files allowed to be open to 1024 since 256 was too few. We called `ulimit -n 1024` to do this for the testacc and testacc-bitbucket targets.
* Changed the start-docker-compose.sh to use the bitbucket server environment variable so that it doesn't always refer to localhost
* Skipped some testcases that are consistently failing in master branch
* Added a version.env file to be used to control the versioning from CICD builds
* Set version to 1.4.0
* In the start-docker-compose.sh if the BITBUCKET_SERVER environment variable is not set then use http://localhost:7990
In the start-docker-compose.sh if the BITBUCKET_SERVER environment variable is not set then use http://localhost:7990
