CAS-14297 : Fix dependency of deconvolve tests
The `test_imgval_startmodel_axesmismatch` tests (for mfs and mtmfs) were
causing the following `test_imgval_startmodel_basic_copy` test to fail.
This is likely because of some shared state between the tests.
The band-aid fix is to make sure the two tests use different image
names, and now all the tests in the deconvolve test suite (except the
asp test) pass. The asp test is also the only one being skipped at the
moment.
The root cause of the interdependency is still to be determined.
