Merge pull request #499 in CASA/casa6 from CAS-13404 to master
* commit 'f36d6103c5b6312afc0dbb431aa9ff229668694e':
rennamed test_linearmosaic.py to test_tool_linearmosaic.py
Added new test_tool_linearmosaic to the component mapping json file. CAS-13404: removed an unused mention of the joint mosaic image CAS-13404: Updated tests after further discussions regarding the expected results. CAS-13404: modified class name for tests, some of the test to an an existing image
removed unnecessary helper imports
removed unnecessary helper imports
test script for linearmosaic tool