test: avoid ambiguity in error reporting

The script contains simple copy-n-paste error where not all the
variables were declared correctly.
tests: make SRM_NOT_SUPPORTED a valid response

SRM_NOT_SUPPORTED is a valid response for many request types.  The
basic tests should not enforce that an SRM implementation supports
all methods.
tests: remove SRM_INVALID_REQUEST as accepted ReserveSpace response.

For ReserveSpace, the requests should be valid, so the SRM instance
should never response SRM_INVALID_REQUEST.  Such return value should
fail a test.