Handle AttributeError in create_from under device_specification.py (#2488) (#2586)
Handle AttributeError in create_from under device_specification.py (#2488) (#2586)

* Raise PulseError when calling create_from on a device that does not support pulse.

create_from in device_specification.py first tries to set the buffer.
However, if the backend does not support pulse it does not have a
default buffer setting which results in an AttributeError. This
commit adds a check to ensure that the backend supports pulse. A
PulseError is raised if the backend does not support pulse.
QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py