Tasks - handling of errors/exceptions in Task::run()

[Chrico]

Is your feature request related to a problem? Please describe.

Currently Tasks are added and executed in Command and on exception we stop the execution. But in some cases like in the SymlinkVipGoDir::run() we do not check for successful execution and continue with an errornous results. In other cases we continue the runner, but printing errors, like in DownloadWpCore:run(). We should generalize this and consider, that "critical execution" needs to 100% succeed or otherwhise throw an Exception to stop the program.

Describe the solution you'd like
Following Tasks need to be updated and throw a custom Exception when we cannot ensure that the task 100% completes:

• SymlinkVipGoDir::run() - Filesystem::relativeSylink - it is required that all are created successfully.
• CopyDevPaths:copySources() - Filesystem::copy - is it required that all are succesfully copied?
• DownloadWpCore::run() - should maybe bubble up to Command ?
• GenerateDeployVersion::writeDeployId() - does internally handle error and just print a message.
• UpdateLocalWpConfigFile::run - prints an error...is this an error or more a notice?
• UpdateLocalWpConfigFile::saveFile() - wp-config cannot be written? Should be required - or?

Additional context
See discussion here: #5

Just had a quick review yet..maybe we'll find more. Will update the list when i find one.