Command-line parameters should be consistently applied when creating tasks

[tjmcs]

When creating tasks, the current version of snapctl only uses the command-line parameters associated with the snapctl task create ... command when a task is being created using a workflow manifest. In the case where a task is being created using a task manifest, any command-line parameters that are included in the snapctl task create ... command are silently ignored.

It would be much less confusing to the user if these command-line parameters were consistently applied for both of these use cases (creating a task using either a task manifest or a workflow manifest), with any command-line parameters that are set by the user when creating a task using a task manifest overriding the corresponding definitions for these parameters in the task manifest.

[tjmcs]

It should be noted that this issue is a more generic statement of Issue #285, which simply requests that users be allowed to override the task name from a task manifest; a PR that resolves this issue would also resolve Issue #285.