* Add support for envFrom, volumeMounts, serviceAccountName, and imagePullPolicy
* Add comments for added functions
* Add test functions for --env-from
* Add test functions for --volume-mount
* Add test functions for --service-account-name and --image-pull-policy
* Add testing functions to cover the case "service update --env-from"
* Add test functions to cover the case "service update --volume-mount"
* Add missing test functions for config_changes.go
* Add testing functions for pkg/util/parsing_helper.go
* Fix a bug on a test case, caused by ignoring random orderedness of map
* Remove image-pull-policy because it is not supported by Knative
* Fix comments to clarify it as well as to fix a typo
* Remove service-account-name flags in order to submit it as a seperate PR
* Split --volume-mount flag into --volume-mount and --volume flags in order to enable multiple times mounting for the same volume
* Change the name of local variable to simplify
* Update docs
* Change the flag "--volume-mount" into "--mount", and fix it to make volume automatically when the config-map or secret is directley used. In addition, the test cases are changed to new unit test style. To keep the original orderedness given via flags, OrderedMap implementation is added as well
* Fix usage descriptions for the mount flag
* Factor out the name existence checking from createEnvFromSource
* Fix the usage description for --mount
* Sanitize a generated volume name
* Add support for service labels with --label or -l
* Add tests
* Fix typo
* Move MapToArray helper method to separate file
* Allow unsetting labels by passing empty value
* Fix test
* Add test case for label removal
* Wrap error message with flag
* Update docs to include --label
* Update labels on both services and revisions
* Add some test cases around weirder user input
* Change unset behavior and allow setting empty env and label
* Update docs for new unset behavior
* Make single keys to map to empty values
* Move helper to util
* Use assert.DeepEqual
* Use new mock test + check both service and revision
* Use new method and correct year
Ying Chun Guo