slice.show() can crash

[sajith]

If we try to show() a slice before submit(), we crash. Consider the below snippet:

from fabrictestbed_extensions.fablib.fablib import FablibManager

fm = FablibManager()
slice = fm.new_slice(name="test-slice")
slice.show()

This fails with:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "./fabrictestbed_extensions/fablib/slice.py", line 168, in show
    data = self.toDict()
           ^^^^^^^^^^^^^
  File "./fabrictestbed_extensions/fablib/slice.py", line 486, in toDict
    "project_id": str(self.get_project_id()),
                      ^^^^^^^^^^^^^^^^^^^^^
  File "./fabrictestbed_extensions/fablib/slice.py", line 842, in get_project_id
    return self.sm_slice.project_id
           ^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'project_id'

Perhaps this could fail a little more gracefully.