Add metadata support for volume

Now able to pass metadata to the create method,
as well as update it with set, and remove it with unset.
I'm currently passing it as an optional param like the following:
--meta-data=key1=value1
which seems weird, what about
--meta-data=key1:value1
I'd have to update type too if that is the case.

Change-Id: I0fc8398768da015c1f53c5c564c68a2cfb53e778
Merge "Add metadata support for volume"