Added -p option to the list command. This alows filtering results by
supported platforms, e.g.
wa list workloads -p linux
Also adding missing supported_platforms attribute to various extensions.
If an extension does not have this attribute, the assumption is that it
is supported by all available platforms.
terminalsize was loaded from a location added to sys.path during
bootstrap. This appeared to be causing import issues. There is no longer
a good reason for terminalsize to be loaded that way, so just moved it
under wlauto.utils so that it can be loaded normally.
